what is life biology essay

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1 Definition of Life

Study guide, learn objectives.

• Identify the core characteristics that define “life.”
• Identify the commonalities and differences among various definitions of “life.”
• Discuss the challenges of settling on a single definition of life.

Key Concepts and Terms

• Sensitivity to stimuli

Reproduction

• Homeostasis
• Growth and development
• Energy processing

Biology is the science that studies life. What exactly is life? This may sound like a silly question with an obvious answer, but it is not easy to define life. For example, a branch of biology called virology studies viruses, which exhibit some of the characteristics of living entities but lack others. Although viruses can attack living organisms, cause diseases, and even reproduce, they do not meet the criteria that biologists use to define life.

From its earliest beginnings, biology has wrestled with four questions: What are the shared properties that make something “alive”? How do those various living things function? When faced with the remarkable diversity of life, how do we organize the different kinds of organisms so that we can better understand them? Finally, what biologists ultimately seek to understand is how this diversity arises and how it continues. As new organisms are discovered every day, biologists continue to seek answers to these and other questions.

Properties of Life

All groups of living organisms share several key characteristics or functions: order, sensitivity or response to stimuli, reproduction, adaptation, growth and development, regulation, homeostasis, and energy processing. When viewed together, these characteristics serve to define life.

Order (Cells)

Cells are considered the most basic units of life because they represent discrete units that can independently embody all of the other characteristics listed below. All life living things consist of one or more cells. Even very simple, single-celled organisms are remarkably complex. Inside each cell, atoms make up molecules. These in turn make up cell components or organelles. Multicellular organisms, which may consist of millions of individual cells, have an advantage over single-celled organisms in that their cells can be specialized to perform specific functions and even sacrificed in certain situations for the good of the organism as a whole. How these specialized cells come together to form organs such as the heart, lung, or skin in organisms like the toad shown in Figure 1  will be discussed later.

Sensitivity or Response to Stimuli

Organisms respond to diverse stimuli. For example, plants can grow toward a source of light or respond to touch ( Figure 2 ). Even tiny bacteria can move toward or away from chemicals (a process called chemotaxis) or light (phototaxis). The movement toward a stimulus is considered a positive response, while the movement away from a stimulus is considered a negative response.

CONCEPTS IN ACTION

Watch this video to see how the sensitive plant responds to a touch stimulus .

Single-celled organisms reproduce by first duplicating their DNA, which is the genetic material, and then dividing it equally as the cell prepares to divide to form two new cells. Many multicellular organisms (those made up of more than one cell) produce specialized reproductive cells that will form new individuals. When reproduction occurs, DNA, which encodes genes, is passed along to an organism’s offspring. These genes are the reason that the offspring will belong to the same species and will have characteristics similar to the parent, such as fur color and blood type.

Growth and Development

All organisms grow and develop according to specific instructions coded for by their genes. These genes provide instructions that will direct cellular growth and development, ensuring that a species’ young ( Figur e 3 ) will grow up to exhibit many of the same characteristics as its parents.

Regulation/Homeostasis

Even the smallest organisms are complex and require multiple regulatory mechanisms to coordinate internal functions, such as the transport of nutrients, response to stimuli, and coping with environmental stresses. For example, organ systems such as the digestive or circulatory systems perform specific functions like carrying oxygen throughout the body, removing wastes, delivering nutrients to every cell, and cooling the body.

To function properly, cells require appropriate conditions such as proper temperature, pH, and concentrations of diverse chemicals. These conditions may, however, change from one moment to the next. Organisms are able to maintain internal conditions within a narrow range almost constantly, despite environmental changes, through a process called homeostasis or “steady state”—the ability of an organism to maintain constant internal conditions. For example, many organisms regulate their body temperature in a process known as thermoregulation. Organisms that live in cold climates, such as the polar bear ( Figure 4 ), have body structures that help them withstand low temperatures and conserve body heat. In hot climates, organisms have methods (such as perspiration in humans or panting in dogs) that help them to shed excess body heat.

Energy Processing

All organisms (such as the California condor shown in Figure 5 ) use a source of energy for their metabolic activities. Some organisms capture energy from the Sun and convert it into chemical energy in food; others use chemical energy from molecules they take in.

The diversity of life on Earth is a result of mutations or random changes in hereditary material over time. These mutations allow the possibility for organisms to adapt to a changing environment. An organism that evolves characteristics fit for the environment will have greater reproductive success, subject to the forces of natural selection.

Evolution by natural selection results in adaptations . All living organisms exhibit a “fit” to their environment. Biologists refer to this fit as adaptation and it is a consequence of evolution by natural selection, which operates in every lineage of reproducing organisms. Examples of adaptations are as diverse as unique heat-resistant Archaea that live in boiling hot springs to the tongue length of a nectar-feeding moth that matches the size of the flower from which it feeds. All adaptations enhance the reproductive potential of the individual exhibiting them, including their ability to survive to reproduce. Adaptations are not constant. As an environment changes, natural selection causes the characteristics of the individuals in a population to track those changes.

Watch the following video to review the characteristics of life. Do the characteristics listed in the video differ from those listed above?

the study of living organisms and their interactions with one another and their environments

Introductory Biology: Evolutionary and Ecological Perspectives Copyright © by Various Authors - See Each Chapter Attribution is licensed under a Creative Commons Attribution 4.0 International License , except where otherwise noted.

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4: What is Life?

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What is biology? In simple terms, biology is the study of living organisms and their interactions with one another and their environments. This is a very broad definition because the scope of biology is vast. Biologists may study anything from the microscopic or submicroscopic view of a cell to ecosystems and the whole living planet. Listening to the daily news, you will quickly realize how many aspects of biology are discussed every day. For example, recent news topics include Zika virus and using a new technology called CRISPR to specifically target and edit human genes. Other subjects include efforts toward finding a cure for AIDS, Alzheimer’s disease, and cancer. On a global scale, many researchers are committed to finding ways to protect the planet, solve environmental issues, and reduce the effects of climate change. All of these diverse endeavors are related to different facets of the discipline of biology.

• 4.1: What makes something living?
• 4.2: Levels of Organization
• 4.3: The Diversity of Life

Thumbnail: Phylogenetic Tree of Life. (CC BY 3.0; Crion via Wikimedia Commons ).

What is life?

• Open access
• Published: 27 July 2021
• Volume 48 , pages 6223–6230, ( 2021 )

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• Jaime Gómez-Márquez   ORCID: orcid.org/0000-0001-6962-1348 1  

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Many traditional biological concepts continue to be debated by biologists, scientists and philosophers of science. The specific objective of this brief reflection is to offer an alternative vision to the definition of life taking as a starting point the traits common to all living beings.

Results and Conclusions

Thus, I define life as a process that takes place in highly organized organic structures and is characterized by being preprogrammed, interactive, adaptative and evolutionary. If life is the process, living beings are the system in which this process takes place. I also wonder whether viruses can be considered living things or not. Taking as a starting point my definition of life and, of course, on what others have thought about it, I am in favor of considering viruses as living beings. I base this conclusion on the fact that viruses satisfy all the vital characteristics common to all living things and on the role they have played in the evolution of species. Finally, I argue that if there were life elsewhere in the universe, it would be very similar to what we know on this planet because the laws of physics and the composition of matter are universal and because of the principle of the inexorability of life.

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Introduction

Life is a wonderful natural process that occurs in highly organized dynamic structures that we call living beings. Today, thanks to the enormous advance of Biology, we know and understand much better the vital phenomenon, the molecular biology of the cells, the enormous biodiversity on our planet, the evolutionary process, and the complexity of ecosystems. However, despite these enormous advances, biology still lacks a solid theoretical framework necessary to understand the vital phenomenon and to answer questions such as what is life? or are viruses living entities? To answer these and other fundamental questions related to life, in addition to the universal laws of physics, biology needs its own principles to help us find answers to major theoretical challenges such as the origin of life, the construction and maintenance of genomes, or the concept of life itself. Regarding the principles governing life, there have been several contributions from different perspectives (e.g. [ 1 , 2 , 3 , 4 , 5 ]) and I myself have proposed a series of principles (named as the commandments of life) to explain and understand the vital phenomenon from an evolutionary perspective, far from any vitalist, pseudo-scientific or supernatural considerations [ 6 ].

In the words of B. Clark, a definition of life is needed more than ever before to provide defendable objective criteria for searches for life on other planets, to recognize critical distinctions between machine life and robots, to provide insight into laboratory approaches to creating test-tube life, to understand the profound changes that occurred during the origin of life, and to clarify the central process of the discipline of biology [ 7 ]. It is worth noting what E. Koonin wrote about the complexity of defining life: “In my view, although life definitions are metaphysical rather than strictly scientific propositions, they are far from being pointless and have potential to yield genuine biological insights” [ 8 ]. However, despite its importance there is no widely accepted definition of what life is and some of the most commonly employed definitions (see below) face problems, often in the form of robust counter-examples [ 5 , 9 ]. Even some scientists and philosophers of science suggest that it is not possible to define life [ 5 , 8 ].

We can define life in very different ways depending on the context and the focus we want to give to the definition. For example, we can define life as the period from birth to death or as the condition that occurs only in living organisms. We can also say that life is a wonderful and ever-changing process that occurs in highly organized receptacles that we identify as living entities. Likewise, the popular encyclopedia Wikipedia define life as “a characteristic that distinguishes physical entities that have biological processes ….. from those that do not …” [ 10 ]. However, with these expressions we are not defining precisely what life is and therefore we need to create a definition that concisely but informatively reflects our scientific knowledge of the vital phenomenon. We have to distinguish between life and living matter, which is the place where life lives, and between living beings and non-living matter. In reality, when we ask ourselves “what is life?” we are asking “what are the characteristics that distinguish a living organism from a non-living entity?

There are numerous definitions of life formulated from different characteristics of living beings (replication, metabolism, evolution, energy, autopoiesis, etc.) and from different approaches (thermodynamic, chemical, philosophical, evolutionary, etc.). Often, definitions of life are biased by the research focus of the person making the definition; as a result, people studying different aspects of biology, physics, chemistry, or philosophy will draw the line between life and non-life at different positions [ 11 ]. These strategies create a panoply of alternative definitions that makes it very difficult to reach a consensus on the best definition of life because they all have pros and cons. [ 12 , 13 ]. Let me briefly discuss some of the most representative definitions of life. There is a short definition “Life is self-reproduction with variations” [ 14 ] that is interesting for its brevity and because it includes two fundamental characteristics of living organisms: reproduction and evolution. However, this minimalist definition is clearly insufficient [ 8 ] and it does not include some of the most important traits we see in living things. Along these lines, there is also the definition coined by NASA: “Life is a self-sustaining chemical system capable of Darwinian evolution” [ 15 , 16 ]. This is a more complete and, I believe, better definition than the previous one, as it incorporates, in addition to reproduction and evolution, metabolism. However, both definitions are unsatisfactory because neither cell nor multicellular organisms are self-sufficient as there is always a dependence on other organisms and external factors to live and reproduce. Furthermore, these definitions say nothing about the chemical nature of living matter, the interactions with the environment or the low entropy of living things. Apart from that, reproduction being essential for the perpetuation of species and evolution, not all living beings are able to reproduce (e.g. the mule, most bees, etc.) and do not thereby lose their living status. A more recent definition of life states: “Life is a self-sufficient chemical system far from equilibrium, capable of processing, transforming and accumulating information acquired from the environment” [ 17 ]. Although this definition is more comprehensive than the previous ones and includes a reference to thermodynamics, in my opinion it has four drawbacks: (i) the term “self-sufficient” is not adequate because the quality of life does not provide self-sufficiency; (ii) the thermodynamic component does not highlight how fundamental low entropy or high order is for any living being; (iii) information can be acquired from “within” and not only from the environment; (iv) life is not a system is a process and living beings are the system where that process occurs (I discuss this point below). From a very different perspective it was defined life as “matter with the configuration of an operator, and that possesses a complexity equal to, or even higher than the cellular operator” [ 18 ]. This proposal introduces a new term, the operator, which is somewhat confusing, excludes viruses and makes a strange classification of living systems. On the other hand, some scientists have also attempted to define life from a handful of key features. Thus, seven “pillars” (the essential principles by which a living system functions) have been proposed on which life as we know it can be defined [ 19 ], but no definition was provided. Life has also been considered as any system that from its own inherent set of biological instructions and the algorithmic processing of that "prescriptive information" can perform the nine biofunctions [ 20 ] which are basically the same as the "pillars" mentioned above. However, no definition of life was proposed, and again it was considered as a system rather than a process. Both definitions exclude viruses as living beings, mainly because the existence of a membrane, a metabolic network and self-replication are set as conditions for life. In short, there are many more definitions of life but as R. Popa says “We may never agree on a definition of life, which will remain forever subject to a personal perspective” [ 21 ].

My definition of life

Traits are measurable attributes or characteristics of organisms and trait-based approaches have been widely used in systematics and evolutionary studies [ 22 ]. Since any definition of life must connect with what we observe in nature, my strategy for finding a definition of life was to establish what are the key attributes or traits common to all living things. What do bacteria, yeasts, lichens, trees, beetles, birds, whales, etc. have in common that clearly differentiates them from non-living systems? In my opinion, living organisms share seven traits: organic nature, high degree of organization, pre-programming, interaction (or collaboration), adaptation, reproduction and evolution, the last two being facultative as they are not present in all living beings.

Organic nature and highly organized structures. Living matter is organic because it is based on carbon chemistry and molecular interactions take place following the laws of chemistry. As R. Hazen wrote “Carbon chemistry pervades our lives. Almost every object we see, every material good we buy, every bite of food we consume, is based on element six. Every activity is influenced by carbon—work and sports, sleeping and waking, birthing and dying.” [ 23 ]. Living organisms are highly organized structures that maintain low entropy (the vital order) by generating greater disorder in the environment, thus fulfilling the postulates of thermodynamics [ 24 , 25 ]; when this vital order is lost, life disappears and the only way to restore life is to generate a new vital organized structure through reproduction [ 6 ]. Living organisms resist entropy thanks to biochemical processes that transform the energy they obtain from nutrients, sun or redox reactions. It could be said that vital order and energy are two sides of the same coin.

Pre-programming. Every living entity has a software (a pre-programme) in its genetic material that contains the instruction manual necessary for both its construction (morphology) and its functioning (physiology). This programme has been modified in the course of evolution, as a consequence of contingency and causality, so it is not a static or immutable program but a dynamic one. Furthermore, there is also another preestablished program that conditions the vital phenomenon and that I have called the principle of inexorability [ 6 ]. Let me give few examples of the principle of inexorability at different levels of complexity. The shape of ribosome is determined (pre-programmed) by the chemical bonds that are established between ribosomal proteins and rRNA. A similar example is the λ phage morphogenesis that depends only on interactions protein–protein and protein-DNA. Evolutionary convergence or the need for wings to fly are other examples of this inexorability guided by the laws of nature.

Interaction and adaptation. If we look at nature in its purest state or at the complex human society, we can see countless interactions between living beings and with their environment necessary for survival and reproduction. We can see interactions at the molecular level (e.g., allosteric interactions, metabolic pathways, cellular signaling, quorum sensing), in the relationships between organisms of the same or different species (e.g., sexual reproduction, symbiosis, infection, parasitism, predator–prey, or sound language), or between living forms and the environment (e.g., photosynthesis or physiological/anatomical interactions for swimming or flying). Interaction is collaboration, it is cooperation at all levels [ 6 ], the ecosystem being the best example of multiple collaborative interactions between very different organisms. In terms of adaptation, living organisms show a great capacity to adapt both to their surroundings and to environmental circumstances; furthermore, adaptations involving new biological characteristics can be seen as an opportunity to find a different way to evolve. In this sense, the evolutionary process reflects this continuous adaptation and anatomy, physiology and genome bear witness to this. Life is adaptative because species adapt to environmental changes modifying their physiology or metabolism, for instance reducing heartbeat during hibernation (e.g. the grizzly bear Ursus arctos horribilis ) or synthesizing fat from excess sugar to increase the energy reserves of the body (e.g. Homo sapiens ). In addition to these temporal adaptations in response to environmental changes [ 26 ], there are also changes in genotype or phenotype since the adaptation process is the result of natural selection acting upon heritable variations [ 27 ]; a well-known example of this is the peppered moth Biston betularia whose allele frequencies of the locus that controls the distribution of melanin in the wings changed with the industrial revolution in England [ 28 ]. Epigenetic variations also contribute to rapid adaptative responses [ 29 , 30 ].

Reproduction and Evolution. Another property of living beings is their ability to perpetuate themselves and thus make it possible for the species not to disappear and to evolve. Reproduction can be observed at the molecular (DNA replication), cellular (mitosis, meiosis, binary division), and organismal (sexual and asexual) levels. From a different perspective, reproduction is also the way to overcome the second law of thermodynamics and the tyranny of time because when we reproduce, we are creating a new order and resetting the vital clock to zero [ 6 ]. What about individuals such as the mule or the male and female of a species, or the hermaphrodite that cannot self-fertilize, who cannot reproduce because they are sterile or because they need another member of their species to reproduce? Are not these organisms living beings? Of course, they are! In this context, reproduction must be considered as a facultative trait because not all living organisms are fertile or can produce offspring on their own but maintain all other traits necessary for the life process. If an individual is sterile, the species will continue to exist because the evolutionary process must be analyzed at the population level, not at the level of individual organisms; obviously, if the entire population were sterile, then the species would disappear and there would be no life. All species have the capacity to evolve, and this property is unique to life. Evolution allows living beings to adapt to new circumstances and the best genomes are selected and transmitted to the next generations. The concept of evolution (reproduction with variations and permanence in time) allows us to interpret the reality of the life we observe now and to guess what it has been like in the past. We cannot predict the future because evolution is not a finalistic process, it is, to use the words of J. Monod, the fruit of chance and necessity.

There is nothing on this planet, apart from a living being, that complies with all these characteristic features of living beings. It should therefore be possible to define life by logically combining them. Consequently, I define life as a process that takes place in highly organized organic structures and is characterized by being preprogrammed, interactive, adaptative and evolutionary. If life is the process, a living organism is the system in which that process takes place and which is characterized as organic, highly organized, pre-programmed, interactive, adaptative, and evolutionary. Why do I say that life is a process and not a system? According to the Merriam-Webster dictionary, a process is a natural phenomenon characterized by gradual changes that lead towards a certain result. A second meaning defines it as a continuous natural or biological activity or function; and a third one as a series of actions or operations conducing to an end. These three meanings of what a process is fit very well with what we observe happening in living beings, which is none other than the vital process or life. The dictionary itself defines a system as a regularly interacting or interdependent group of items forming a unified whole, and as an assemblage of substances that is in or tends to equilibrium or a group of body organs that together perform one or more vital functions. Once again, these definitions fit very well with what a living being represents.

What is the difference between life, living being and a robot? [ 31 ] Life is the vital process and the living being is the system, the “container” in a metaphorical way, where the vital process takes place. Following this reasoning, a robot would be an artificially organized, pre-programmed and interactive system, but unlike a living being it is not alive because it is neither organic, nor does it reproduce, adapt, or evolve. A robot or a population of robots cannot “reproduce and evolve” on its own, without the intervention of its "creator" (the human being), it will always need to be built or programmed by an engineer to do so. I do not dispute that the robot can adapt, especially thanks to advances in artificial intelligence, although I am not sure that it can do so in the biological sense of the term. Biological adaptation is a process by which a species eventually adapts to its environment as a result of the action of natural selection on phenotypic characteristics [ 32 ]. A robot may be able to adapt to its environment, but what it cannot do is adapt itself through a selective process (without intervention from its creator) and change into a new type of robot (evolve). On the other hand, regarding the synthetic lifeforms named as xenobots [ 33 ], I think they cannot be considered as pure robots, but as an interface between living beings and artificial robots, as they are made from cells. In the future we will probably build robots so perfect that we can consider them as almost living beings and as the result of the intervention of a creator (their engineer), something that we cannot say about living beings unless we are creationists.

Are viruses alive?

A. Turing, one of the pioneers in the development of computer sciences, wrote: “Can machines think? This should begin with definitions of the meaning of the terms “machine” and “think” [ 34 ]. To paraphrase Turing, we could ask ourselves: can viruses be considered living entities? And the answer to this question, so important for biology and still controversial [ 35 ], is to define what a virus is and what life is. At least from a theoretical point of view, biology should seek a clear and definitive answer to this question instead of adopting a skeptical attitude and assuming what K. Smith wrote in his classic book on viruses, “As to the question asked most frequently of all, are viruses living organisms? that must be left to the questioner himself to answer” [ 36 ].

Viruses are entities that straddle the boundary between living and non-living and therefore their biological status is controversial. A virus can be defined as an acellular infectious agent whose structure consists of a macromolecular complex of proteins and nucleic acids. Viruses are not cells, they do not metabolize substances, nor can they reproduce by themselves, grow, or breathe. Yet, regardless of whether we consider viruses to be living beings or not, they are an inescapable part of life and there is an undeniable biological connection between the virus and the organism it infects. Given the close interconnection between viruses and their hosts, it seems plausible that viruses play essential roles in their hosts [ 37 ]. For example, endogenous retroviral elements have shaped vertebrate genome evolution, not only by acting as genetic parasites, but also by introducing useful genetic novelty [ 38 ]. More recently, it was found in the human genome a gene regulatory network based on endogenous retrovirus that is important for brain development [ 39 ] and a new tamed retroviral envelope that is produced by the fetus and then shed in the blood of the mother during pregnancy [ 40 ].

Viruses are capsid-encoding particles that infect all kind of cells and share hallmark genes with capsidless selfish genetic elements, such as plasmids and transposons [ 41 ]. Traditionally, they have been regarded as lifeless agents because they have no metabolism of their own and need a cell to replicate and generate new viruses [ 42 ]. However, while this is true, I believe that this is not a definitive criterion for excluding them from the tree of life (more on this below). There are scientists in the opposite side that consider viruses as living beings that can evolve [ 43 ] and classify them as capsid-encoding organisms as opposed to the ribosome-encoding organisms that include all cellular life forms [ 37 , 44 ]. Viruses have played a key role in the evolution of species [ 35 ] because they are the most abundant source of genetic material on Earth, are ubiquitous in all environments, and have actively participated in the exchange of genes or DNA fragments with their hosts [ 41 , 45 , 46 ].

We cannot say whether a virus is a living thing or not without defining what is life and what is a living thing. Obviously, if we take the cell as the minimum vital unit, we cannot consider viruses as living entities, and any discussion of this is superfluous. As far as I am concerned, considering viruses as non-living creatures because they need a cell to reproduce is not a very strong argument for two reasons. First, viruses are obligate intracellular parasites, and, like all parasites, they use the host for their own benefit, and this is their survival strategy. Viruses need nothing else to pursue the same goal as all species on this planet, which is to generate more viruses better adapted to infect new organisms. They apply the “law of least effort” to achieve this goal and may even decide to remain inside the host cell in a lysogenic manner, as in the case of bacteriophage lambda [ 47 ], or by establishing latency as herpesviruses do [ 48 ]. Second, as I said before no cell or organism is self-sufficient, as it needs at least a supply of food/energy to survive and reproduce. We know that life is absolutely interdependent. For example, we depend directly on our intestinal bacterial flora for our survival, and indirectly on nitrogen-fixing bacteria or photosynthesis. We could take to absurdity the argument that because viruses need a cell to reproduce, they are not alive and say that a man or a woman is not a living being because they cannot reproduce by themselves. The argument that a virus is not a living thing because it is an inert entity outside the cell is also not valid because such a virus could still have the ability to infect cells. Similarly, a spore or a seed cannot be considered lifeless because it is inert, as it is only waiting for the right environmental conditions to germinate, and that wait can last for thousands of years.

To answer the question of whether viruses are alive or not, I base my argument in support of considering viruses as living entities obviously on my own definition of life (this paper), as well as on what we know about the biology of viruses. First, viruses, like all cellular entities in nature, are composed of organic molecules; a virus consists of a nucleic acid (DNA or RNA), which is its genetic material as in all living things, and a protein capsid encoded by the viral genome that protects the viral genetic material and participates in the propagation of the virus in the host; viral capsids show fascinating dynamics during the viral life cycle [ 49 ]. Secondly, viruses are highly organized structures. There is an astonishing diversity of organization and geometric design of viruses, requiring only a few different structural subunits of the capsid to construct an infectious particle. Many viruses have developed very successful self-assembly systems; so much so that the viral capsid can self-assemble even outside the host cell [ 50 ]. The third feature common to all living things is that they are pre-programmed, and viruses also fulfill this characteristic because in their genetic material are written the instructions to make new viruses capable of infecting new cells or organisms. Viruses in their genome have the necessary (though not sufficient because they need elements provided by the host cell) instructions to make new viruses, and in this they are the same as any other living thing. In addition, the process of self-assembly to generate new viruses occurs spontaneously because the instructions to do it autonomously are both in the capsid-forming molecules themselves and in the nucleic acid, either DNA or RNA [ 49 ].

Two other characteristics of living organisms are the ability to interact with other living organisms (interaction) and to adapt genetically to new circumstances (adaptation). Viruses interact with their host in multiple ways: during infection, when their genes are expressed and their genome replicated, when virions are formed, when they integrate into the genome of the host cell, or when they engage in horizontal gene transfer processes. Viruses not only interact with their host, but also adapt by generating new variants that increase their ability to infect other cells, or by taking control of cell metabolism for their own benefit, or even to escape the immune response [ 51 ]. In terms of reproduction and evolution, which are two closely related processes, viruses reproduce in the host cell and evolve through changes in their genome. Viral evolution, like that of all living things, refers to the heritable genetic changes that a virus accumulates during its life cycle, which may arise from adaptations in response to environmental changes or host immune response. Because of their short generation times and large population sizes, viruses can evolve rapidly [ 52 ].

Microbiologist and Nobel laureate J. Lederberg said that “The very essence of the virus is its fundamental entanglement with the genetic and metabolic machinery of the host”. As far as I am concerned, this statement is essentially true and its profound meaning is, at least for me, further proof that viruses are living things. Viruses form part of many integrated biological systems, and they played an important role in the evolution of species [ 53 ]. They can exchange genetic material and participate in horizontal gene transfer [ 43 ] even between individuals from different species [ 54 ]. Due to their high frequency of mutation [ 55 ], viruses are so abundant in nature and present such a high degree of diversity that they constitute by themselves the virosphere [ 46 ]. This great viral biodiversity is proof that these living entities perform fundamental evolutionary and ecological functions [ 56 , 57 ]. In conclusion, I believe that viruses should be considered as living entities that can participate in events as diverse as causing pandemics, destroying bacteria, causing cancer, or participating in horizontal gene transfer.

Following the metaphor of the “container” as the vessel or system (the living being) in which the life process takes place, the fact that viruses are obligated intracellular parasites and do not have a cellular structure and metabolism of their own does not seem to fit this metaphor. It is obvious that the virus cannot be the “container” where the life process takes place, since the virus, when outside the cell, is in a “dormant” state waiting to find a suitable host to infect and complete its life cycle; we could say that it is inert but not yet dead. Therefore, in the special case of viruses, the “container” is the cell. Once the virus finds its specific “container”, it can then reproduce, or integrate into the genome of the host cell, or remain as an episome, or intervene in the evolutionary process through exchange of genetic material. From genomic and metagenomic data, we know that co-evolution between viral and host genomes involves frequent horizontal gene transfer and the occasional co-option of novel functions over evolutionary time. We can say that viruses and their cellular hosts are ecologically and evolutionary intertwined [ 58 ].

I would like to refer to an interesting reflection on the defining characteristics of life and how viruses fit into this conceptual framework [ 59 ]. Thus, Dupré and O'Malley consider collaboration as a common criterion of life and I can only agree with this assessment; in this sense, in a previous paper on the principles that govern life [ 6 ], I use the expression “cooperative thrust” to refer to the importance of collaboration in the origin and evolution of living beings. Without considering collaboration or cooperation as a key interaction, we could not explain endosymbiosis, eukaryogenesis, metabolism, multicellularity, etc. In the present paper, collaboration is implicit in what I call interaction as a common and fundamental feature of all living things. Interestingly, these authors point out that “leaving viruses out of evolutionary, ecological, physiological or conceptual studies of living entities, would allow only an incomplete understanding of life at any level” [ 59 ]. Considering this emphasis on collaboration as a sine qua non condition for life, how does the world of viruses fit in? Dupré and O'Malley propose, and I agree, that viruses can be understood as alive when they actively collaborate (I mean when they are infecting the target cell) and when they do not collaborate (I would say they are inactive), they have at most a potential for life.

Finally, I would like to add that I am aware that there are many scientists who consider that viruses are not living beings basically because they do not have a cellular structure with all that this means. Therefore, this biological dilemma will probably be with us for a long time to come. I think it will only be resolved when we reach a consensus on what life is because only then will we be able to say categorically whether something is alive or not. This is what I have modestly tried to do in this paper.

What would life be like elsewhere in the universe?

The massive number of exoplanets strongly suggests that there is a high probability that life evolved elsewhere in the universe. Astrobiologists are committed to the search for life in the cosmos and for that purpose it is very convenient to have a criterion about what life is [ 16 ]. How can we be sure that there is life on a distant planet? To do so, we need to define some biosignatures that can establish the possible existence of living things elsewhere in the universe [ 60 ], otherwise what are we looking for? In addition to this, it would also help a lot in this search for life on other planets, finding out how life began on Earth.

Some scientists and philosophers of science think that this preconception of what life is may be a problem rather than a solution in the search for life in other planets. C. Cleland in her book about the nature of life states, “Life is not the sort of thing that can be successfully defined. In truth, a definition of life is more likely to hinder than facilitate the discovery of novel forms of life” [ 5 ]. I do not entirely agree with this double statement because although we must be open-minded in the search for life outside our galactic home, at the same time I think it is a good idea to have a hypothesis based on the only certainty we have about vital phenomena, which is life on Earth, that will help in the design of the search for extraterrestrial life.

Is there life elsewhere in the universe? We don't know yet and it is probably only a matter of time before we find life on other planets or aliens find us. In my opinion if there is life elsewhere in the universe, it will most likely be similar to what existed, exists or will exist on our planet. Let us see why. First of all, the laws of physics and chemistry are universal and these laws, directly or indirectly, govern everything that happens with the matter of the universe. According to the cosmological principle, the same physical laws and models that applies here on Earth also works in all parts of the universe [ 61 ]; it is also assumed that physical constants (gravitational constant, speed of light, etc.) remain the same everywhere in the universe. Second, the elements that make up the matter of the stars are the same everywhere in the universe although in different proportions; the “periodic table” is the same for the whole universe. Whether life exists elsewhere in the universe based on a chemistry other than carbon we do not know and can only speculate, but what we do know for sure is that life on Earth is based on carbon chemistry, perhaps because it cannot be otherwise. Third, there is the aforementioned principle of inexorability [ 6 ]. In this context, what does this principle mean? It means that if the environmental conditions are suitable, glucose will be converted into pyruvate in an aqueous medium, chemiosmotic processes will be an important mechanism for generating chemical energy, flying organisms will have wings, or genetic information will be encoded in a language analogous or identical to what we know on Earth. According to this, the differences between the Earth living forms and the “space creatures” could be attributed to a different evolutionary stage or to specific environmental conditions. This hypothetical premise could be very important when developing projects that seek life elsewhere in the universe.

Dhar PK, Giuliani A (2010) Laws of biology: why so few? Syst Synth Biol 4:7–13

Article   PubMed   Google Scholar  

Lane N (2015) The vital question. Profile Books, London

Google Scholar  

Shou W, Bergstrom CT, Chakraborty AK, Skinner FK (2015) Theory, models and biology. eLife 4:e07158

Article   PubMed   PubMed Central   Google Scholar  

Cockell CS (2017) The laws of life. Phys Today 70:43–48

Article   CAS   Google Scholar  

Cleland CE (2019) The quest for a universal theory of life. Cambridge University Press, Cambridge

Book   Google Scholar  

Gómez-Márquez J (2020) What are the principles that govern life? Commun Integr Biol 13:97–107

Clark B (2019) A generalized and universalized definition of life applicable to extraterrestrial environments. In: Kolb VM (ed) Handbook of astrobiology. CRC Press, Boca Ratón

Koonin EV (2012) Defining life: an exercise in semantics or a route to biological insights? J Biomol Struct Dyn 29:603–605

Article   CAS   PubMed   Google Scholar  

Cleland CE, Chyba CF (2002) Defining life. Orig Life Evol Biosph 32:387–392

Wikipedia (2021) Life. Wikipedia, the free encyclopedia.

Szostak J (2012) Attempts to define life do not help to understand the origin of life. J Biomol Struct Dyn 29:599–600

Article   CAS   PubMed   PubMed Central   Google Scholar  

Luisi PL (1998) About various definitions of life. Orig Life Evol Biosph 28:613–622

Popa R (2003) Between necessity and probability: searching for the definition and the origin of life. Springer, Berlin

Trifonov EN (2011) Vocabulary of definitions of life suggests a definition. J Biomol Struct Dyn 29:259–266

Joyce GF (1994) Forward. In: Deamer DW, Fleischaker GR, Sudbury MA (eds) Origins of life: the central concepts. Jones and Bartlett, Burlington

Benner SA (2010) Defining life. Astrobiology 10:1021–1030

Vitas M, Dobovišek A (2019) Towards a general definition of life. Orig Life Evol Biosph 49:77–88

Jagersop Akkerhuis GA (2010) Towards a hierarchical definition of life, the organism, and death. Found Sci 15:245–262

Article   Google Scholar  

Koshland D Jr (2002) The seven pillars of life. Science 295:2215–2226

Abel DL (2012) Is life unique? Life 2:106–134

Popa R (2012) Merits and caveats of using a vocabulary approach to define life. J Biomol Struct Dyn 29:607–608

Gallagher R, Falster DS, Maitner BS et al (2020) Open science principles for accelerating trait-based science across the Tree of Life. Nat Ecol Evol 4:294–303

Hazen RH (2019) Symphony in C: carbon and the evolution of (almost) everything. WW Norton & Co., New York

Schneider E, Sagan D (2005) Into the cool: energy flow, thermodynamics, and life. University of Chicago Press, Chicago

Peterson J (2012) Understanding the thermodynamics of biological order. Am Biol Teach 74:22–24

Somero GN, Lockwood BL, Tomanek L (2017) Biochemical Adaptation: response to environmental challenges from life’s origins to the Anthropocene. Sinauer Associates, Sunderland

Gardner A (2009) Adaptation as organism design. Biol Lett 5:861–864

Mueller L (2020) 1973 The evolution of melanism. In: Mueller L (ed) Conceptual breakthroughs in evolutionary ecology. Academic Press, Cambridge

Schmid MW, Heichinger C, Coman Schmid D et al (2018) Contribution of epigenetic variation to adaptation in Arabidopsis . Nat Commun 9:4446

Article   PubMed   PubMed Central   CAS   Google Scholar  

Gómez-Schiavon M, Buchler NE (2019) Epigenetic switching as a strategy for quick adaptation while attenuating biochemical noise. PLoS Comput Biol 15(10):e1007364

Bongard J, Levin M (2021) Living things are not (20th century) machines: updating mechanism metaphors in light of the modern science of machine behavior. Front Ecol Evol 9:650726

Bock WJ (1980) The definition and recognition of biological adaptation. Am Zool 20:217–227

Kriegman S, Blackiston D, Levin M, Bongard J (2020) A scalable pipeline for designing reconfigurable organisms. Proc Natl Acad Sci USA 117:1853–1859

Turing AM (1950) Computing machinery and intelligence. Mind 59:433–460

Koonin EV, Starokadomskyy P (2016) Are viruses alive? The replicator paradigm sheds decisive light on an old misguided question. Stud Hist Philos Biol Biomed Sci 59:125–134

Smith K (1962) Viruses. Cambridge University Press, Cambridge

Dupré J, Guttinger S (2016) Viruses as living processes. Stud Hist Philos Biol Biomed Sci 59:109–116

Katzourakis A, Gifford RJ (2010) Endogenous viral elements in animal genomes. PLoS Genet 6:e1001191

Brattas L, Jönsson ME, Fasching L et al (2017) TRIM28 controls a gene regulatory network based on endogenous retroviruses in human neural progenitor cells. Cell Rep 18:1–11

Article   PubMed   CAS   Google Scholar  

Heidmann O, Béguin A, Paternina J, Berthier R, Deloger M, Bawa O, Heidmann T (2017) HEMO, an ancestral endogenous retroviral envelope protein shed in the blood of pregnant women and expressed in pluripotent stem cells and tumors. Proc Natl Acad Sci USA 114:E6642–E6651

Koonin EV, Dolja VV (2014) Virus world as an evolutionary network of viruses and capsidless selfish elements. Microbiol Mol Biol Rev 78:278–303

Moreira D, López-García P (2009) Ten reasons to exclude viruses from the tree of life. Nat Rev Microbiol 7:306–311

Forterre P (2010) Defining life: the virus viewpoint. Orig Life Evol Biosph 40:151–160

Raoult D, Forterre P (2008) Redefining viruses: lessons from mimivirus. Nat Rev Microbiol 6:315–319

Gilbert C, Cordaux R (2017) Viruses as vectors of horizontal transfer of genetic material in eukaryotes. Curr Opin Virol 25:16–22

Zhang Y-Z, Shi M, Holmes EC (2018) Using metagenomics to characterize and expanding virosphere. Cell 172:1168–1172

Casjens SR, Hendrix RW (2015) Bacteriophage lambda: early pioneer and still relevant. Virology 479–480:310–330

Nicoll MP, Proença JT, Efstathiou S (2012) The molecular basis of herpes virus latency. FEMS Microbiol Rev 36:684–705

Bruinsma RF, Wuite GJL, Roos WH (2021) Physics of viral dynamics. Nat Rev Phys 3:76–91

Baschek J, Klein H, Schwarz US (2012) Stochastic dynamics of virus capsid formation: direct versus hierarchical self-assembly. BMC Biophys 5:22–40

Agudelo-Romero P, Carbonell P, Perez-Amador MA, Elena SF (2008) Virus adaptation by manipulation of host’s gene expression. PLoS ONE 3(6):e2397

Duffy S, Shackelton LA, Holmes EC (2008) Rates of evolutionary change in viruses: patterns and determinants. Nat Rev Genet 9:267–276

Koonin EV, Dolja VV (2013) A virocentric perspective on the evolution of life. Curr Opin Virol 3:546–557

Faria NR, Suchard MA, Rambaut A, Streicker DG, Lemey P (2013) Simultaneously reconstructing viral cross-species transmission history and identifying the underlying constraints. Phil Trans R Soc B 368:20120196

Duffy S (2018) Why are RNA virus mutation rates so damn high? PLoS Biol 16:e3000003

Rohwer F, Prangishvili D, Lindell D (2009) Roles of viruses in the environment. Environ Microbiol 11:2771–2774

O ́Malley MA (2016) The ecological virus. Stud Hist Philos Biol Sci 59:71–79

Harris HMB, Hill C (2021) A place for viruses on the tree of life. Front Microbiol 11:604048

Dupré J, O’Malley MA (2009) Varieties of living things: life at the intersection of lineage and metabolism. Philos Theor Biol 1:e003

Jheeta S (2013) Final frontiers: the hunt for life elsewhere in the universe. Astrophys Space Sci 348:1–10

Keel WC (2007) The road to galaxy formation, 2nd edn. Springer-Praxis, Berlin, Heidelberg

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I would like to thank my colleagues M. L. González Caamaño and R. Anadón for their useful discussions. This work is dedicated to my parents.

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Gómez-Márquez, J. What is life?. Mol Biol Rep 48 , 6223–6230 (2021). https://doi.org/10.1007/s11033-021-06594-5

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The essence of life

• Wentao Ma   ORCID: orcid.org/0000-0003-2948-7695 1  

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Although biology has achieved great successes in recent years, we have not got a clear idea on “what is life?” Actually, as explained here, the main reason for this situation is that there are two completely distinct aspects for “life”, which are usually talked about together. Indeed, in respect to these two aspects: Darwinian evolution and self-sustaining, we must split the concept of life correspondingly, for example, by defining “life form” and “living entity”, separately. For life’s implementation (related to the two aspects) in nature, three mechanisms are crucial: the replication of DNA/RNA-like polymers by residue-pairing, the sequence-dependent folding of RNA/protein-like polymers engendering special functions, and the assembly of phospholipid-like amphiphiles forming vesicles. The notion “information” is significant for us to comprehend life phenomenon: the life form of a living entity can just be defined by its genetic information; Darwinian evolution is essentially an evolution of such information, transferred across generations. The in-depth analysis concerning the essence of life would improve our cognition in the whole field of biology, and may have a direct influence on its subfields like the origin of life, artificial life and astrobiology.

This article was reviewed by Anthony Poole and Thomas Dandekar.

Accompany with the development of molecular biology, which was marked at its origin by the discovery of the double helix structure of DNA (in 1953) [ 1 ], we have gained a tremendous amount of knowledge about the “secret” of life [ 2 ]. However, ironically, we are still uncertain about the essence of life, which can be manifested by the fact that to date even a consensus on the definition of life cannot be reached [ 3 , 4 ]. In fact, the essence of life represents one of the several long-standing fundamental concerns of ours over the whole field of the natural sciences. As a case in point, the question “what is life?” was adopted as the title of Schrödinger’s famous pamphlet [ 5 ] – the author was a physicist himself; and notably, it was published (in 1944) even about a decade before we began to dig into the “secret of life” (i.e., the rise of molecular biology).

The two distinct aspects of the concept “life”

Why we cannot reach a common opinion on the definition of life, though there have been numerous relevant discussions, or disputations? Now, the reason is not that we still lack some knowledge concerning the life phenomenon or the mechanisms underlying, but that we have not realized there are two distinct aspects for the concept of life, which is just a problem of logic.

We want to define “life” because we feel it is obviously different from the “non-life background”. For example, life can “replicate”, generating offspring, which is called the feature of “reproduction” in terms of biology (note: an idea emphasizing the difference between the two terms will be mentioned below when we talk about the implementation of life). Related to this feature, the specificity of an offspring individual is by and large derived from its parent(s), which is known as the feature of “heredity”; but the specificity of an offspring individual is not completely derived from its parent(s), which is relevant to the feature of “variation”. Perhaps more impressively, all living things we observe nowadays are leading, in its environment, a life style rather in favor of their survival and reproduction, which is referred to as the feature of “adaption”. All the features mentioned so far point to one essential aspect of life phenomenon: Darwinian evolution. “Reproduction”, manifesting “heredity” and “variation”, is the prerequisite of Darwinian evolution, whereas “adaption” is the result of Darwinian evolution.

But it isn’t over. Life is obviously different from its non-life background also in another aspect. It appears that any organism nowadays is a quite complicated system that “self-sustains”, involving energy and matter exchange with its environment. For example, a plant can absorb light energy and raw materials, and an animal may feed on plants to gain energy and raw materials it needs. Those biochemical reactions exploiting the energy and materials within the organism (to synthesize its own components), as a whole, is termed “metabolism”. Finally, “waste products” derived from the metabolism would be eliminated into the environment. If the organism “dies”, all these events, associated with the self-sustainment, would no longer occur. Concerning the wording “self-”, we should annotate a little more. Indeed, in accordance with the second law of thermodynamics, by the energy and matter exchange with its environment a living system can be sustained (or say, the order of the system can be kept) — this seems to be a feature of living systems. However, there are certainly also other open systems that are sustained in order, termed “dissipative systems”, such as Rayleigh–Bénard convection, Belousov-Zhabotinskii reaction, turbulence, cyclone, etc. The distinctive characteristic of a living system lies in that it is “self-sustained”, which means the energy-matter-exchange and the biochemical reactions involved in the metabolism are active events, depending upon the system’s own “functional components” (e.g., across-membrane transporters and enzymes).

Of course, the two aspects are associated with each other. For contemporary life, the functional components depending on which a living system can self-sustain are typically made of proteins (for possible primordial life in the hypothetic “RNA world”, the functional components were made of RNA [ 6 – 9 ]). No doubt, it is just Darwinian evolution that has given rise to these functional components. In fact, we may explain the whole tendency concerning such an evolution in a general way. Energy and raw materials are always the targets of competition in Darwinian evolution, thus always being in shortage. When a variation occurs resulting in the appearance of a function which enables the system to make use of more “fundamental” energy and raw materials (which are abundant), the variation would be maintained by natural selection. With the “in-depth” proceeding of such a tendency, more and more relevant functions would emerge, e.g., those catalytic functions might be organized into “metabolic pathways” finally. Thus, the system would become more and more complex and look increasingly “self-sustaining” – it, for instance, may ultimately be able to exploit rather “fundamental” energy such as sunlight and rather “fundamental” materials such as water, carbon dioxide and minerals. Of course, beyond the tendency to exploit more fundamental energy and material, which gives rise to anabolism, a living system may also develop the ability to exploit the “ready-made” energy and materials by feeding on other living systems, which brings about catabolism. Indeed, we could say that the self-sustainment is actually one manifestation of the life’s feature “adaptation”. That is, the second aspect that makes life distinctive – “self-sustaining”, is actually a result of the first aspect that makes life distinctive – “Darwinian evolution”.

Remarkably, a relatively popular definition of life, which was phrased by NASA, serving as a “working definition” for searching extraterrestrial life, says: “Life is a self-sustaining chemical system capable of undergoing Darwinian evolution” [ 10 – 12 ]. It is popular perhaps because it catches both the two aspects of life. However, the definition is essentially defective (which reflects well a common confused understanding on the concept of life). The people conceiving this expression did not realize that the two aspects are completely different from each other – so different that they even cannot be described in the same context. How can an individual system undergo Darwinian evolution? Darwinian evolution makes sense only for a lineage (from the level of population to that of species and that above). Or rather, Darwinian evolution does not refer to the evolution of an entity, but to the evolution of the form of that entity. In fact, if we accept the meaning of “evolution” as “becoming different over time”, we get to know that this kind of “evolution in form”, involving replication (reproduction) of individuals, means the descendant individuals become different from their ancestral individuals, rather than the alteration of a living individual itself. That is to say, in accordance with the two distinctly different aspects of the concept of life, the definition should split, as some expression like: “A life form is a matter form capable of undergoing Darwinian evolution; a living entity is a self-sustaining chemical system – in nature, it results from the Darwinian evolution and might engage into further Darwinian evolution”. In this definition, the word “life” is associated with the aspect of “Darwinian evolution”, and is in regard to a “form”; the word “living” is associated with the aspect of “self-sustaining”, and is in regard to an “entity”. See Table  1 for several examples concerning the application of such a definition.

In addition, there is a supplementary note to the definition. Logically, there should be an “intermediate” concept between the “life form” and the “living entity”. That is the entity which carries a life form, or say, the entity with a form capable of undergoing Darwinian evolution. We may call it a “life entity”, or a “Darwinian entity”. When we use the latter name, we emphasize that such an entity might engage in Darwinian evolution. By using the former name, we can realize directly the difference and relationship between the words “life” and “living” adopted here – conceptually, a living entity is just a complex life entity, in which the character of “self-sustaining” is developed, as explained above. Certainly, in practice, most life entities could be viewed as living entities because they should be more or less “self-sustaining”, except for those appearing in the very beginning of life (some supposition about relevant situations will be mentioned below), as well as those extremely simple parasites like viruses (see Table  1 ).

Certainly, given that “self-sustaining” has a blurry sense and the feature is derived from Darwinian evolution in nature, one that cannot endure a complex definition may be more satisfied with the definition of life with an emphasis on Darwinian evolution. That is, concisely, we may just define the “life form” mentioned above as the concept “life” itself: “Life is the form capable of undergoing Darwinian evolution” – but surely, one must bear in mind that, in this simplified definition,“self-sustaining”, a feature concerning “living” in our common sense, has not been reflected.

Three key chemical mechanisms supporting the implementation of life

Above we have interpreted the concept of life according to its two distinctive aspects. However, under the topic concerning “the essence of life”, it would be better to inquire into the mechanisms in nature that render the implementation of the two aspects possible.

How can an entity engage into Darwinian evolution? As already mentioned, “replication/reproduction”, manifesting the characteristics of “heredity” and “variation”, is the prerequisite of Darwinian evolution. Here we consider this point in more detail. The entity should be capable of replicating with some extent of variation, and the variation should be inheritable (which means it can be passed on to the following generations). In the contemporary living world, such a kind of replication is mainly rooted in the template-directed copying of DNA (except for in some viruses and viroids, RNA instead), and in the hypothetic RNA world [ 6 – 9 ], such a kind of replication is rooted in the template-directed copying of RNA. No matter how, the underlying chemical mechanism is the base-pairing between the monomers of nucleic acids, in which hydrogen bonds play a crucial role. Indeed, this mechanism of “modular replication” [ 13 ] (polymer-replicating through template-directed copying based on monomer-pairing) meets the requirements mentioned above regarding the variable replication and inheritable variation exactly. It seems to be a “magical mechanism” in nature that makes the implementation of life possible. To date, no other mechanism has been “found” or “envisioned” to be able to satisfy these requirements, although there have been some efforts attempting to realize this mechanism on other molecules, such as some polymers akin to the nucleic acids [ 7 , 14 ], and even some special organic molecules designed ad hoc [ 15 ].

However, the mechanism of “modular replication” is not adequate for the implementation of Darwinian evolution. Even if an entity can replicate with inheritable variation based on this mechanism, no natural selection would occur merely due to this feature, because the selection acts on the level of “phenotype” rather than that of “genotype”. That is to say, there must be corresponding functions derived according to the nucleic acid sequenceand, relevantly, corresponding functional alterations stemmed from the variations of the sequence. In the contemporary living world, the functions are mainly carried by proteins translated from mRNAs, which are in turn transcribed from the genes carried by DNA (except for in some cases, functions are carried directly by “functional RNAs”, transcribed from DNA). In the hypothetic RNA world, all the functions were carried by RNA, the same material carrying genes [ 6 – 9 ]. No matter how, a key mechanism that ultimately makes such a shift toward phenotype possible is: a molecule of the functional polymer (protein or RNA), in fact, folds to its special structure with its special function “according to” its special sequence. For the folding of the proteins, the hydrophobic interaction plays a crucial role; for the folding of the RNAs, hydrogen bonds (leading to intra-chain base-pairings) play a crucial role. In addition, noticeably, for the implementation of the second aspect of life, this mechanism also deserves enormous credit – it is just such structure-based functional polymers that could support the “self-sustaining” (e.g., enzymes; or ribozymes for an “RNA-based organism”), no else. Indeed, this mechanism, i.e., the sequence-dependent folding of RNA/protein-like polymers, which brings about corresponding special functions, seems to be a second “magical mechanism” in nature that renders life possible to arise.

Moreover, there is a third mechanism that is also very important for the implementation of life. Indeed, considering RNA molecules might both implement the modular replication and fold to carry functions, they, as individual molecules, may have been the simplest, earliest “Darwinian entities” (i.e., “life entities”). For example, some RNA species that can benefit its own replication, such as the one catalyzing the RNA replication (i.e., an RNA replicase ribozyme) [ 7 , 14 ] and/or the one catalyzing the synthesis of its building blocks (i.e., a nucleotide synthetase ribozyme) [ 7 , 16 ], may have emerged, say, in the beginning of the RNA world. However, more advanced entities that can harvest multiple advantages simultaneously should represent the subsequent direction of evolution. In nature, typically one functional molecule bears only one function – the reason has been implied in the second mechanism explained above: a functional polymer folds to its special structure with its special function according to its special sequence. That means a more advanced entity should have to comprise multiple functional molecules (e.g., both the RNA replicase ribozyme and the nucleotide synthetase ribozyme), which cooperate with each other. Hence, there should be a mechanism to keep these different functional molecules sufficiently adjacent. In this regard, it seems that no mechanisms can work better than the one suggested by our modern living cells: encompassing the functional molecules within a lipid vesicle [ 17 ] – this mechanism limits the movement/dispersal of the cooperating functional molecules and meanwhile, perhaps equally importantly, does not limit the spatial movement/dispersal of the resulting entities as integral individuals (see Ref. [ 18 ] for a more detailed discussion on the so-called “protocells”). The formation of the vesicle, with its membrane composed of amphiphilic molecules such as fatty acids and phospholipids, is a natural process occurring in water, wherein, again, the hydrophobic interaction plays a key role. Notably, it has been suggested that while those RNA-like modular-replicating entities are called replicators, such more advanced, cell-like entities should be referred to as “reproducers” [ 13 , 19 ]. So the process of the reproduction contains the replication of replicators within the vesicle and the subsequent division of that vesicle. From then on, at the level of individual occurs no replication but reproduction (see the next section for a remark about more complicated reproduction when life form became more complex). This attempt to conceptually distinguish reproduction from replication reflects well the significance of the “vesicle” mechanism in regard to the first aspect of life – enabling the most fundamental step of life form’s evolution toward complexity, from the molecular level to the level above molecule (see Table  2 for a supplemental annotation to this point). In addition, remarkably, we can also tell the great significance of this mechanism in regard to the second aspect of life – it naturally “defines” a closed, independent system, based on which the so-called “self-sustaining” could make sense; and on the other hand, the system is not absolutely closed, which allows the matter-energy-exchange that is critical to the sustainment ( according to the second law of thermodynamics). Indeed, this mechanism concerning the formation of lipid vesicles, which gives rise to cell-like entities, seems to be the third “magical mechanism” in nature that makes the emergence of life possible.

Finally, it should be noted that we are not overstating when we say all these chemical mechanisms may ultimately be ascribed to the features of those building blocks available. Undoubtedly, the formation of vesicle is owing to the feature of the phospholipids-like molecules, i.e., “amphiphilicity”; as mentioned already, the implementation of modular replication should be attributed to the feature of nucleotides/deoxynucleotides; apparently, the implementation of functions in the functional polymers is also determined by the feature of corresponding building blocks – amino acids for proteins and nucleotides for RNA. Indeed, just because the types of amino acids are more than those of nucleotides and the chemical property of the amino acids are more active than that of nucleotides, proteins, rather than RNA, act as the main functional molecules in modern life. As a more straightforward contrast, it is just the additional 2’-OH in nucleotides that determines that RNA is more suitable to act as functional molecules but less suitable to act as template molecules than DNA.

Understanding life in terms of information

As mentioned above, when we talk about the evolution of life, we do not mean the evolution of individual entities but the evolution of their life forms. Actually, we can interpret such an “evolution in form” this way: a living entity bears and is characterized by its life form, and when it reproduces, it passes its life form on to its offspring; the life form evolves over generations, mainly ruled by the mechanism of Darwinian selection (more rigorously, here we should talk about “life entities vs. their life forms”, as explained in the section above concerning their definitions). See Table  3 for an example illustrating the significance of this notion. Indeed, to comprehend the characteristic of the life phenomenon, it is very important to clearly distinguish the form of an entity from the entity itself. Here, we can talk about this issue in more depth.

Let us start with the case of molecules. In regard of “matter”, two molecules, as independent entities, are certainly different from each other. But we also often say two molecules are of the same “kind”, e.g., two water molecules. Notably, the main aim of the science chemistry is just to explore the interactions/reactions between various “kinds” of molecules. In fact, generally speaking, the “kind” of a molecule just means the form of the molecule. This is easy to understand. Remarkably, there is a sort of special molecules in nature – the polymers constructed by monomer residues of several or more distinct types. Admittedly, when we talk about these polymers, we have in our minds those central biomolecules – DNA, RNA and proteins, or something alike. For such molecules, their forms are “sensitively” affected by their residue sequences – even the variation of a single residue at a certain locus can bring about molecules of different kinds. Actually, the form of such a polymer can be defined by the form of its residues and the sequence of the residues. Here it is notable that the sequence, manifesting as a succession of different “letters”, is just a typical “format” of “information”. That is, “information”, as a “quantifiable” notion in some way, may help us to define the “kinds” or “forms” of these “sensitive” polymers. We can say, for instance, that the form of a DNA molecule is just specified, or represented, by the information carried on its sequence (here we have predefined the molecule as DNA, so the form of its residues, i.e., nucleotide, is definite and needs not to be included in the statement).

Now we turn to the case of living entities. A living entity tends to be a complex system composed of many molecules (especially if we do not consider the situation in the very beginning of life as mentioned above). Likewise, two of such entities are certainly different in regard of matter because they are independent of each other. And similarly, it appears that they can also be of the same “kind”, e.g., two individuals of the same species. However, typically, two living entities cannot be completely identical in form, unlike two molecules in the chemical world. Indeed, the differences within the same species have accumulated generation by generation. Then, what is the essence of the accumulated differences? With little dispute, we can boil it down to the sequence of genomic DNA (or RNA sometimes), or say, as explained above, the information carried on this “sensitive” polymer. Surely, it is just the “genetic information” in terms of biology. In fact, due to some causes (e.g., the environmental isolation), the differences of the genetic information within a species may increase further, ultimately giving rise to different species – this is just the manner how the whole living world has arisen and is still evolving forward. In other words, we can say that the form of a living entity is in practice defined by its genetic information – it is this information that ultimately determines all the specificity of the living entity. Indeed, as somewhat few exceptional cases, two or more living entities might as well be “identical in form” – and this is just because their genetic information is “identical”, e.g., monozygotic twins (or multiples) and those clone-individuals.

Here we have traced the form of living entities into the form of, thus the information carried on, their genetic molecules (the so-called “sensitive” polymers, DNA or RNA). The genetic information is transferred across generations by the modular replication, and transferred within a generation via expression into the functional molecules (also the so-called “sensitive” polymers, proteins or RNA) – that is just what the Central Dogma tell us. Then, it is natural selection that closes the circle – acting on the phenotypes “figured” by the functional molecules and gives rise to further genetic information deserving transferring across generations (a more detailed explanation on this point will appear below). Additionally, see Table  4 for an interesting remark on the “strategy” of using the genetic information (to transfer life form), in regard to the emergence of complex living entities.

In fact, “information” is in itself a concept without a clear definition, and the reason seems to be similar to that for the concept of life – there are two distinct aspects for “information”: first, it represents something different from others (or say, background); second, it makes meaning someway. To make the situation more confusing, the meaning of information is dispensable in some context – indeed, as noted in the classic document concerning information communication [ 20 ], when information is transferred, only the specificity represented by the information is important. Nonetheless, genetic information in life could find its explanation with regard to the concept “information” in such a context. Firstly, the sequence of genomic DNA/RNA distinguishes the entity from others clearly. Secondly, the sequence makes meaning in respect that it may be expressed into proteins/RNA, functioning in favor of the entity’s survival/reproduction (in short, “adaption”). Thirdly, not all the sequence in the genome makes meaning – surely, there are nonsense areas, especially in eukaryotes; the sequence in these areas, though meaningless, does contribute to the identification of the entity from others; and no doubt, when the genetic information is transferred to the next generation (by the modular replication of genomic DNA/RNA), whether it has meaning or not is unimportant.

All in all, we can understand that the “evolution in form” concerning life (i.e., Darwinian evolution) is actually an evolution of information. In fact, Darwinian evolution constitutes a natural way to generate information: first, a mutation during the replication of the genome gives rise to a distinction; then, the distinction, favoring the living entity’s survival/reproduction or not, is subject to natural selection; if the result is positive, the new information would be “fixed” into the genome, maintained across generations. More explicitly, for instance, the natural selection can work this way: supposed that a residue at a position of the genomic DNA turns out to be “A”, rather than “T”, “C”, or “G”, and this specificity, by manifesting as phenotype, provides this individual with some advantages in “adaption”; then, this letter at this position may be maintained in the genome generation after generation. Indeed, as it is understood, selection resolves “uncertainty” and thus generates information [ 20 ] – in the living world, it is natural selection that generates genetic information. This is by and large right, except for a notation that if the mutation is “neutral”, the specificity may also be maintained in the genome across generations until the position mutates again – such “provisional genetic information” is most likely to occur in the nonsense areas of the genome mentioned above. No matter how, we can make a general statement that it is mainly natural selection, performing over numerous generations, that leads to the accumulation of genetic information in the genome of living individuals, resulting in our prosperous living world comprising numerous life forms.

Noticeably, it is just such a special relation between life and information that constitutes the root of that distinctive field: “bioinformatics”. No “chemo-informatics” or “physico-informatics” is comparable.

Conclusions

“Life” is a concept with two completely distinct aspects: Darwinian evolution and self-sustaining. An effort to define “life” should describe the two aspects separately, as some expression like: “A life form is a matter form capable of undergoing Darwinian evolution; a living entity is a self-sustaining chemical system – in nature, it results from the Darwinian evolution and might engage into further Darwinian evolution”. Alternatively, on account of that “self-sustaining” has a blurry sense and it is derived from Darwinian evolution in nature, one that pursue a clear and concise definition may be more satisfied with a statement only emphasizing Darwinian evolution, like: “Life is the form capable of undergoing Darwinian evolution”.

Regarding its implementation in nature, life seems to be a miracle, owing to three magical chemical mechanisms (to realize its two aspects): the replication of DNA/RNA-like polymers by residue-pairing, the sequence-dependent folding of RNA/protein-like polymers engendering special functions, and the assembly of phospholipid-like amphiphiles forming vesicles.

The life form of a living entity can be defined in terms of information – that is, its genetic information; natural selection is the key to give rise to such information, which has accumulated over numerous generations.

The dissection about the essence of life would improve our cognition on the whole discipline of biology, “deepening” its “success” nowadays. More generally, it may promote our fundamental understanding on natural phenomena further. More particularly, it may have a direct influence on the fields like the origin of life, artificial life and astrobiology.

Reviewers’ comments

I am grateful to the reviewers for their thoughtful analysis and comments on the manuscript. I think that the topic of this manuscript, which addresses a long-standing, controversial issue with respect to the most fundamental concept in the field of biology, is very suitable to appear in this journal, which has a policy to publish reviewers’ comments and authors’ responses together with the manuscript. I hope that the paper would aid in improving the situation that we, as researchers in the field of life sciences, unfortunately, are still hesitating about what on earth is “life”.

Reviewer 1: Anthony Poole, Stockholm University, Sweden

Reviewer comments.

I am fine with the main argument. However, it is not new to the literature, and is not as crisply delivered as previous treatises, including some which the author cites.

Author’s response: It is fine that the reviewer endorses the main argument of the paper. As for the novel contents of the paper, it will be shown in my following responses that the paper does tell something new to the literature.

This philosophical piece by Wentao Ma is a discussion of the definition of life. Ma covers well-trodden territory, arguing primarily for a Darwinian definition of life.

Author’s response: Indeed, an important aspect concerning the discussion about the essence of life is to provide a clear definition of life, as it has been done here (see the section “The two distinct aspects of the concept ‘life’”). Just considering the awkward situation that not even a clear definition of “life” can appear in any textbook of biology, such an effort is of great significance. However, that is not all. Even when we can define the concept life in one or several sentences, e.g., using terms like “Darwinian evolution” and “self-sustaining”, we may still wonder about how such processes or features can be implemented in nature. This concern, turning from the “conceptual basis” to the “material basis” of life in nature, should also be included into the topic of “the essence of life” (see the section “Three key chemical mechanisms supporting the implementation of life”). Finally, once we can discern the form of life from living entities, and be aware of the material (chemical) basis of life – particular in regard of those biopolymers, we will comprehend why “life” is deeply associated with another fundamental concept in nature, “information”; and this comprehension, in turn, will no doubt promote our understanding of life phenomenon (see the section “Understanding life in terms of information”).

In addition, though it is attractive to endorse a pure Darwinian definition of life, as explained when I introduce the alternative definition “Life is the form capable of undergoing Darwinian evolution” in this paper, here it should be noted that the availability of “self-sustaining” is rather important regarding the outcome of Darwinian evolution, as we can see in our modern living world. Without this aspect, the life forms would have stayed at a rather simply level, perhaps too trivial to be distinguishable from the background non-living world. Such an understanding may be useful for our efforts in the field of astrobiology.

While I don’t particularly disagree with the main points, the paper really doesn’t cover any new ground, and in my view, other papers do a better job of dealing with this topic. For instance, Szathmáry makes a very helpful distinction between replicators and reproducers [ 19 ]. In contrast, Ma uses the terms replication and reproduction interchangeably. This is not helpful and serves to blur an important distinction between these. The point made by Ma, that life requires three ‘mechanisms’ (replication of a template, generation of functional molecules, and a physical boundary) is fine, but not new, and does not advance current thinking. This is nicely articulated in Ganti’s chemoton model, which consists of three parts (metabolic system, system for heritable control, a boundary system) [ 21 ]. Importantly, the chemoton model led to the concept of infrabiological systems (see [ 19 ]), which lack one of these three components, and is a helpful formulation for understanding the emergence of life. Mix [ 22 ] provides clearer categorical definitions than Ma, who is primarily interested in Darwinian evolution. Ma draws a distinction between ‘life form’ and ‘living entity’, where the first seems to be ‘Darwin life’ and the second is ‘Haldane life’ by Mix’s definitions. Note that Mix provides a third definition that neatly enables us to categorise all cellular life as ‘Woese life’, and also notes that multiple definitions may be applied to some entities. Finally, it is unfortunate that Ma uses the term ‘magic’ in several places - this is both vague and unhelpful. I would encourage the author to take the time to rethink their article with reference to the works [ 19 , 21 , 22 ] (as well as those cited within these key works).

Author’s response: Thank to this journal’s policy that publishes reviewers’ comments and authors’ responses, and also thank to this reviewer’s careful remarks, here we have the chance to discuss these interesting issues related to the manuscript.

Firstly, I have noticed the efforts to make a distinction between replicators and reproducers [ 19 ] (earlier in [ 13 ]). As explained by Szathmáry and his coworkers, new individuals of replicators arise by copying, whereas those of reproducers do not. Life may have originated as replicators (e.g., some RNA species) and evolved into reproducers when they were encapsulated by vesicles (e.g., RNA-based protocells). Then the process of reproduction should contain the replication of replicators within the vesicle and the subsequent division of that vesicle. When the “organisms” became more complex, the process of reproduction would become more complicated, tied with the process of “development”. In the original version of the manuscript, to be more focused, I did not mention this idea. But after rethinking the manuscript with reference with this idea (as suggested by the reviewer), I find that this idea is in fact fairly related to our topic (i.e., “the essence of life”) – with respect to how life, especially those complex life forms, can be implemented in nature. So I have mentioned this idea and added relevant remarks in the new version (see the penultimate paragraph of the section “Three key chemical mechanisms supporting the implementation of life” and Table  4 in the section “Understanding life in terms of information”). Thank the reviewer very much for his kind suggestion.

Secondly, I have also noticed Ganti’s chemoton model [ 21 ], which has been discussed in detail in Szathmáry’s papers mentioned above [ 13 , 19 ]. In my opinion, the model is more like an “empirical model”, which is only summarized from the life phenomena we can observe in appearance. That is, it does not reflect why the three parts (metabolic system, system for heritable control, a boundary system) are essentially required. On the contrary, here I start from the two fundamental aspects of life (Darwinian evolution and self-sustaining) and explain the essential roles of the three “mechanisms” (replication of a template, generation of functional molecules, and a physical boundary). Tracing into the conceptual basis and the material basis of life is just one important novelty of the present paper. Noticeably, just owing to this distinction of the starting point, we can see an important difference between these two ideas. “Generation of functional molecules” is not completely paralleled with “metabolic system” – in fact, only a portion of the functional molecules were involved in metabolism, which supports the self-sustaining. This is apparent in modern life, e.g., numerous proteins serves as structural blocks, rather than enzymes. Indeed, as indicated in this paper, self-sustaining is only one (not all) outcome of Darwinian evolution. Also due to such a standpoint, regarding the infrabiological systems, I tend to think that heritable control is indispensible – that is, an infrabiological “metabolic + boundary” system during the emergence of life is impossible. Additionally, here we can see that the Ganti’s chemoton model, as a typical idea in the field of the origin of life, attempts to summarize the sense of Darwinian evolution and self-sustaining in the same context, without discerning life form from living entities. Such a situation has brought about quite a lot of confusions and controversies in the field. The attempt to rectify this situation just represents the most important novelty of this paper.

Thirdly, I thank the reviewer for bringing the paper [ 22 ] to my attention. In this paper, initially, Mix criticized the recently “popular” viewpoint that definitions of life are impossible or impractical. I endorse the author’s opinion completely. Then it was suggested that since it is difficult to reach a consensus on the definition, we should pursue provisional definitions for clear communications. This also seems to be a correct attitude, because we need to tell other people clearly what we mean when we mention the word “life” (especially in the fields of the origin of life, artificial life and astrobiology). First, he suggested the life closed to modern cellular life can be referred to as Woese life, owing to Woese’s original work that related them by similarities in their rRNA. In my opinion, this summarization, like the chemoton model, is directly phenomenon-based, at least unhelpful for us to envision the essence of life. Then, he introduced “Darwin life – exhibiting evolution by natural selection” and “Haldane life – exhibiting metabolism and maintenance”. Apparently, the author has recognized that there are two completely distinct aspects for life, but he did not associate this recognition with the essence of life. As he wrote in the paper, “Our categories need not be essential or substantial, only methodologically useful” – “Woese life, Darwin life, and Haldane life” are only used to “represent clear categories about which we can make unambiguous statements without committing to whether they are ‘life’ in any larger sense”. More importantly, the author and all other people with similar insights (see the paper and references therein for details) failed to realize the distinction of “form” and “entity” in relation to the life phenomenon. That is, Darwin life should be actually in respect of the “kinds”, i.e., the life forms, whereas Haldane life should refer to individuals, i.e., living entities. Indeed, I would like to say to Mix that bringing his understanding of the distinction between “Darwin life” and “Haldane life” to the level of the essence of life, the provisional definitions may turn into an ultimate one.

Finally, as to the term “magic”, I want to express the idea that it is far from an easy thing to implement life in nature – in regard to the two aspects of life, Darwinian evolution and self-sustaining (that is, it is nearly a miracle). The idea is helpful for us to understand that why we can find only one type of life on the earth, i.e., the one materially based on DNA/RNA/proteins and lipid vesicles, which is often referred to as “life as we know it”. Moreover, this annotation should also aid in our efforts to search “extraterrestrial life”. This seems to be out of question. So I guess the reviewer means that the noun “magic” which is used to refer to the three key chemical mechanisms is not suitable. Therefore, I have changed the noun “magic” to the phrase “magical mechanism” in relevant places.

Reviewer 2: Thomas Dandekar, Department of Bioinformatics, University of Wuerzburg, Germany

First of all, why am I reviewing this manuscript so fast? Well, there is nothing more important than the essence of life, so I have also time to review this. However, working on this topic and getting non-trivial results is far from easy. My impression is that in this article we have a clear, non-trivial distinction between two processes essential for life: (i) Darwinian Evolution versus (ii) the self-sustaining capability of life. The author nicely points out that a distinction of both central features of life leads to further insights. I liked the article, it is thoughtful and so I added some thoughts on it and hope they will improve the already nice piece of work.

Author’s response: Yes, the reviewer’s interpretation of the central idea of this manuscript is almost perfect. Many thanks for the reviewer’s warm comments.

I have the following helpful comments for this nice commentary: The author should incorporate some other perspectives on this. This can easily be done, few sentences are enough as the insightful commentary should be kept short, to make nice reading: a) Explain the notion of information better, as this interestingly always depends on who reads this information. So here, as rightly stated, this information arises by selection and so this type of information is only possible to come about by feature (i) active evolution (more information on this including some insights on how “meaning” develops by such processes as subjective phenomenon can be found in https://opus.bibliothek.uni-wuerzburg.de/frontdoor/index/index/docId/2749 ).

Author’s response: “Information” is another concept without a clear definition, the reason of which seems also to be that it contains two distinct aspects: first, it represents something distinct from others; second, it makes meaning someway. To make things worse, as mentioned in the classic document of information communication [ 20 ], the second aspect, i.e., the meaning of information, is sometimes dispensable. In the manuscript, to be more focus and avoid unnecessary controversy in this respect, I, deliberately, did not explain the notion of information in detail. However, as noticed by the reviewer, it seems hard to evade this point under the explicit subtitle “Understanding life in terms of information”. So I have tried to talk about these fundamental points of “information” and associate them with genetic information and Darwinian evolution in the new version (see the antepenultimate paragraph and the penultimate paragraph of this section). Certainly, readers may see the web site provided by the reviewer for a more extensive discussion on relevant topics. Thank the reviewer for his kind suggestion.

b) The “magical chemical process”: Yes, rightly observed. This happens as there is also the feature (iii) of self-organizing processes. Only in a world where such processes exist in sufficient extent life is possible and such things as the three magical chemical processes come about. So please mention this basic feature of a world in which life is possible. It would be fair to mention here Stephen Jay Gould who spoke about “the exaptive excellence of spandrels…” to explain the power of building blocks [ 23 ]. So, for such magic to happen, suitable building blocks are necessary, they determine which “game” can be played by evolution (insight by Stephen Jay Gould) - in fact seriously limiting the play and its contents, for instance our life will be relying on DNA as information storage and that limits certain “games” we can achieve by our evolutionary processes. My contention would be that the building blocks have to be with some self-organizing capabilities (as amply shown also by other authors on this topic).

Author’s response: Yes, I agree with the reviewer. So I add a table ( Table  2 ) and a paragraph at the end of the section “Three key chemical mechanisms supporting the implementation of life” to mention these points. Note that, to be more focused, I have constrained the sense of “building blocks” – here only in regard to the three key chemical mechanisms mentioned in the text, i.e., nucleotides/deoxynucleotides, amino acids and phospholipid-like amphiphilic molecules.

c) If you follow the argument (“b”), the building blocks are so critical, you appreciate even more, that with human civilisation a new factor appears: you are sufficiently complex to leave the limitations of building blocks, in particular you can build machines and cars, you can establish artificial intelligence, so new technical processes, which do not have the limitation of the building blocks, and (showing the non-trivial insight of the article) these technical processes first improve feature (ii) self-sustaining capabilities of life (simple example: air conditioning when it is too hot in summer, achieved by a machine), and as the feature (ii) is critical for life and evolution of technical apparatus just started, we have currently problems arising from our technical civilisation and clearly, you can also investigate feature (i), evolutionary capabilities in technical processes, e.g. evolution of software, of computers, of cars etc. One can argue if you look at this, whether after all our building blocks are the key feature of life here on earth, to separate this type of life (according to the definitions of the author) from the features of our technology using other building blocks, but trying to fulfill also the two aspects of life discussed by the author but only starting to achieve this in a satisfactory way.

Author’s response: I appreciate the reviewer’s interpretation on the significance of the building blocks in a general sense. I also admire the author’s marvelous extension of the meaning of the two key features of life. In particular, it is interesting to envision that “life form” can finally leave the limitation of building blocks in a chemical sense, blending into human civilisation – a real information-ruled world. These ideas are thoughtful but perhaps run beyond the scope of our current topic. Let us enjoy the policy that allows readers to see the reviewer’s idea along with the author’s.

Abbreviations

National Aeronautics and Space Administration

Watson JD, Crick FHC. A structure for deoxyribose nucleic acid. Nature. 1953;171:737–8.

Article   CAS   PubMed   Google Scholar  

Watson JD, Berry A. DNA: The Secret of Life. New York: Knopf Doubleday Publishing Group; 2003.

Google Scholar  

Deamer D. Special Collection of Essays: What is Life? - Introduction. Astrobiology. 2010;10:1001–2.

Article   PubMed   Google Scholar  

Trifonov EN. Vocabulary of definitions of life suggests a definition. J Biomol Struct Dyn. 2011;29:259–66.

Schrödinger E. What is life? Cambridge: Cambridge University Press; 1944.

Gilbert W. The RNA world. Nature. 1986;319:643.

Article   Google Scholar  

Joyce GF. The antiquity of RNA-based evolution. Nature. 2002;418:214–21.

Bernhardt HS. The RNA world hypothesis: the worst theory of the early evolution of life (except for all the others). Biol Direct. 2012;7:23.

Article   CAS   PubMed   PubMed Central   Google Scholar  

Higgs PG, Lehman N. The RNA World: molecular cooperation at the origins of life. Nat Rev Genet. 2015;16:7–17.

Joyce GF. Foreword, in Origin of Life. In: Deamer DW, Fleischaker GR, editors. The Central Concepts. Boston: Jones and Bartlett; 1994.

Luisi PL. About various definitions of life. Orig Life Evol Biosph. 1998;28:613–22.

Benner SA. Defining Life. Astrobiology. 2010;10:1021–30.

Article   PubMed   PubMed Central   Google Scholar  

Szathmáry E, Maynard-Smith J. From replicators to reproducers: The first major transitions leading to life. JTheor Biol. 1997;187:555–71.

Robertson MP, Joyce GF. The origins of the RNA world. Cold Spring Harb Perspect Biol. 2012;4:a003608.

Tjivikua T, Ballester P, Rebek JJ. Self-replicating system. J Am Chem Soc. 1990;112:1249–50.

Article   CAS   Google Scholar  

Ma WT, Yu CW, Zhang WT, Hu JM. Nucleotide synthetase ribozymes may have emerged first in the RNA world. RNA. 2007;13:2012–9.

Schrum JP, Zhu TF, Szostak JW. The origins of cellular life. Cold Spring Harb Perspect Biol. 2010;2:a002212.

Ma WT, Feng Y. Protocells: At the interface of life and non-life. Life. 2015;5:447–58.

Szathmáry E. The origin of replicators and reproducers. Phil Trans R Soc Lond B Biol Sci. 2006;361:1761–76.

Shannon CE, Weaver W. The Mathematical Theory of Communication. Urbana and Chicago: University of Illinois Press; 1949.

Gánti T. The principles of life. Oxford: Oxford University Press; 2003.

Book   Google Scholar  

Mix LJ. Defending definitions of life. Astrobiology. 2015;15:15–9.

Gould SJ. The exaptive excellence of spandrels as a term and prototype. Proc Natl Acad Sci U S A. 1997;94:10750–5.

Koshland JDE. The seven pillars of life. Science. 2002;295:2215.

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Acknowledgements

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The author’ researchis supported by the National Natural Science Foundation of China (No. 31170958 and No. 31571367).The funding bodies took no part in the design and analysis of the study or in the writing of the manuscript.

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WTM conceived the study and wrote the paper.

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Ma, W. The essence of life. Biol Direct 11 , 49 (2016). https://doi.org/10.1186/s13062-016-0150-5

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Published : 26 September 2016

DOI : https://doi.org/10.1186/s13062-016-0150-5

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Module 1: Introduction to Biology

Introduction to characteristics of life, what you’ll learn to do: list the defining characteristics of biological life.

Biology is the science that studies life, but what exactly is life? This may sound like a silly question with an obvious response, but it is not always easy to define life. For example, a branch of biology called virology studies viruses, which exhibit some of the characteristics of living entities but lack others. It turns out that although viruses can attack living organisms, cause diseases, and even reproduce, they do not meet the criteria that biologists use to define life. Consequently, virologists are not biologists, strictly speaking. Similarly, some biologists study the early molecular evolution that gave rise to life; since the events that preceded life are not biological events, these scientists are also excluded from biology in the strict sense of the term.

From its earliest beginnings, biology has wrestled with these questions: What are the shared properties that make something “alive”? And once we know something is alive, how do we find meaningful levels of organization in its structure?

• Introduction to Characteristics of Life. Authored by : Shelli Carter and Lumen Learning. Provided by : Lumen Learning. License : CC BY: Attribution
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Free Biology Essay Examples & Writing Tips

Don’t know what to write about in your essay on biology? Looking for good biology essay examples for inspiration? This article has all you need!

A biology essay is a type of academic paper that focuses on a particular topic of biology. It can discuss animal life, cycles in biology, or a botanic subject. You will need to demonstrate your critical thinking skills and provide relevant evidence to support your perspective.

On this page, you will find examples of biology essays. You will also find here tips and topics prepared by our experts . They can assist you in nailing your short or extended essay.

Areas of Research for Biology Essays

If you’ve been assigned to write a biology essay, you probably know which area of research you have to choose. However, it might be beneficial to explore other available scopes. It’s useful for both interdisciplinary study and the cases when you are free to pick your area of research. In this section, let’s figure out what you can study in biology.

Here are biological areas of research you should be familiar with:

• Cancer Biology studies this type of disease to prevent, detect, diagnose and cure it. The ultimate goal of such biologists is to eliminate cancer.
• Cell Biology is a branch that studies the structure, function, and behavior of cells. Here, biologists study healthy and sick cells to produce vaccines, medication, etc.
• Biochemistry is an application of chemistry to the study of biological processes on cell and molecular levels. It is a cross-discipline between chemistry and biology. The focus is on the chemical processes of living organisms.
• Computation Biology is a study of biological data that develops algorithms and models to understand biological systems. Here, scientists either work for institutions or research for private enterprises.
• Genetics is an area that focuses on the study of genes and genetic variations for health benefits. It looks at the way DNA affects certain diseases.
• Human Disease is an area within which scientists study different diseases. The field covers cancer, developmental disorders, disease genes, etc.
• Immunology is a branch of biology that focuses on immunity. Immunologists look at the way the body responds to viruses as a way to protect the organism.
• Microbiology studies all living organisms that are too small for our eye to see. It includes bacteria, viruses, fungi, and other microorganisms.
• Neurobiology is the study of the nervous system. Biologists examine the way the brain works and look into brain illnesses.
• Stem Cell and Developmental Biology seeks to examine how the processes behind stem cell’s ability transform cells. The biologists in this area use the power of stem cells to model human illnesses.

Essay on Biology: Writing Tips

Want to know how to start a biology essay? Wondering about the best way to write your essay on biology? Then check out the following tips.

When you’re writing about biology, pay attention to the following features:

• Introduction . Just as in any other form of academic writing, the first section of your paper introduces the subject. Here, explain why your ideas are relevant to biology as a science.
• Thesis Statement. The final one or two sentences of the first paragraph should include your original hypothesis and experiment. You will be proving them in the main body. You do not have to include the results as the reader will encounter them later. If you’re struggling with this part, try our thesis generator .
• Main Body. In this part, write about all the experiments in detail. Often, teachers require to include visual aid to prove your point. For Zoology, Anatomy, Botany, it is pretty easy to find some photos and illustrations.
• Conclusion. Here, restate your thesis. Reemphasize the most critical aspects described in the main body. You can do it by using our summarizing tool . The goal of this last paragraph is to leave an everlasting impression on the reader.

Thank you for reading our article. We hope you found it helpful. Share it with your class peers who also study biology. Additionally, have a look at the biological essay examples below.

812 Best Essay Examples on Biology

Grass and its importance, the benefits of animals to humans essay.

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Biology of Grasses: Description and Importance

The effect of temperature on amylase activity.

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Ubiquity of Microorganisms

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Effects of Vinegar on the Germination Rate of Mung Beans Seeds

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Anaerobic Respiration and Its Applications

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Bronfenbrenner’s Bioecological System Theory

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Seed Germination Experiment: Results and Discussion

Mung seed germination patterns under varying ph values, browning reactions explained, dark or light skin: advantages and disadvantages, botany and taxonomy of the onion.

• Words: 2414

Mitosis and Meiosis in Onion Root Tip

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Strawberries History

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Pets and people

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Aspects, Importance and Issues of Biodiversity

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• Words: 1127

Transpiration Process in Plants

The c-fern plant laboratory experiment.

• Words: 1101

Lemon, Its Origin and Production

• Words: 1115

Osmosis Through a Potato Slice Dipped in Solutions of Varying Concentrations

• Words: 1075

Description of Mitosis and Meiosis

Eukaryotic and prokaryotic cells: key differences, importance of the brain in human body, dugesia, a planarian with its peculiar characteristics.

• Words: 3207

Microbiology: Zygomycota, Ascomycota and Basidiomycota

Characteristics of adult development.

• Words: 1311

Vitamin A: Description and Usage

Mitosis in onion root and whitefish blastula, ethnobotanical uses of plants.

• Words: 1938

Vaquita – Endangered Species

• Words: 1367

Cell Organelles, Their Functions, and Disease

• Words: 1195

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The insect effect on human life, wildlife management and extinction prevention in australia.

• Words: 2902

Biochemistry Dogmas and Their Impacts on Biotechnology

A study of the brine shrimps and their natural environment.

• Words: 1937

Olfactics and Its Importance for Living Beings

• Words: 1446

The Thermoregulation Is and Its Importance

Responsible house plant keeping.

• Words: 2262

Corn Plant’s Developmental Stages

Photosynthesis and cellular respiration, common biochemical cycles, basic and applied biology: key differences, the human family tree development, is earthworm beneficial or harmful to humans, the characteristics and importance of nervous system.

• Words: 1705

Climate Change and Threat to Animals

Understanding the effects of quantity of light on plants growth.

• Words: 1089

Life in the Bottom of the Ocean and Its Protection

• Words: 1529

Pollutants Effects on Cellular Respiration Rate

• Words: 1434

Archaea and Bacteria Prokaryotes Dichotomous Keys

Different ecosystems and living things, molecular biology. production of pet28b and egfp clones.

• Words: 4609

Biology: Analysis of Egg Experiment

Nervous system: the main functions, biology lab report: biodiversity study of lichens, microbial growth and effect of ph on it.

• Words: 1330

Homeostasis and Regulation in the Human Body

Ubiquity of bacteria: laboratory activity.

• Words: 1496

The Integumentary and the Skeleton System

• Words: 1100

Digestion, Absorption and Assembly of Proteins

• Words: 1456

Co-Evolution: Angiosperms and Pollinating Animals

Consequences of orange juice on the germination of mung bean seeds, photosynthesis as a biological process, forensic procedures: hairs and fibres.

• Words: 2067

Microbiological Methods for Assessing Soil Quality

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Telescope and Microscope Discovery Combo

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The Function and Structures of the Human Heart

Anaerobic capacity: power endurance and fatigue index, invertase enzyme: description and role.

• Words: 1151

The Digestive System in the Human Body

Falling in love as part of natural selection.

• Words: 1085

Operant and Respondent Conditioning

Non-trophic interaction in marine species, digestive journey of cheeseburger, environmental microbiology overview.

• Words: 3298

Natural Sciences. The Phenol Red Broth Test Experiment

• Words: 1156

The Brain: Structure and Functions

The process of a prenatal child’s development, plant growth and development with music, reproductive isolation and its potential effects, marine life in united arab emirates.

• Words: 1474

Cane Toad: Introduction and Threat

• Words: 1018

History Of Biotechnology

• Words: 1908

Earth Atmospheric Evolution

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Whether or Not Human Cloning Should Be Allowed

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Yeast and the Fermentation Process

Lipids: fatty acids and glycerols, the effect of different shampoos on the bacteria growth.

• Words: 1737

Psychophysics: Definition & Fundamentals

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Evolution of Predator and Prey Pairings

History of potatoes, their vatiety, and popularity.

• Words: 1233

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The importance of sleeping and dreaming, case study: human body water balance, membrane hands-on laboratory report.

• Words: 1176

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• Words: 1315

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The anatomy and physiology of the nervous system of a rat.

• Words: 1612

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Vertical stratification, introduction to the nervous system, planting bamboo: the role of photosynthesis, paired box 6 (pax6) analysis.

• Words: 1249

Essays About Biology: Top 5 Best Examples and 6 Prompts

Writing essays about biology can be difficult because it’s composed of many subtopics. Check out this article for our top essay examples and writing prompts.

Biology came from the Greek words “bios” (life) and “logos” (study). It’s why biology is the study of life or living organisms. Aside from being a natural science, it also has consolidated themes, such as cells making all organisms. Because it’s a broad topic, biology is divided into specialized fields such as botany, genetics, zoology, microbiology, medicine, and ecology. 

Biologists consider living beings’ origin, evolution, growth, function, structure, and distribution. It’s a comprehensive subject, so there are many things you can write about in your essay. However, at the same time, you might find it challenging to focus on just one area. 

Below are examples to give you an idea of how to write your essays about biology:

1. Essay About Biology by Kelli Wilkins

2. my interests in biology by anonymous on essaywriting.expert, 3. essay on the importance of study of biology by akhila mol, 4. what biology means to me by anonymous on studymode.com, 5. how my biology teacher changed my perspective of learning the subject by sankalan bhattacharya, 1. biology in my everyday life, 2. something i realized because of biology, 3. my memorable biology class experience, 4. genetics’ role in people’s diseases, 5. my experience during the pandemic, 6. biology and health.

“Studying Biology is important for a number of reasons, but in particular because it is used in every field. If we did not have a good understanding of Biology then nobody would be able to understand how bodies work, and how life on earth functions.”

Wilkins shares her desire to study anatomy, a branch of biology, and expounds on what makes biology an essential field. Because biology lets people know more about the world, she digs into why she’s interested in anatomy, specifically to find ways to cure illnesses and develop technologies to discover new treatments. She ends her essay by relating biology to the existence of doctors and hospitals. 

“It is known that education plays an important role in the life of any individual. It gives an opportunity to develop personality and gain specific skills, to get profound knowledge and experience in order to apply them practically in the future. As for me, my major goal is to study Biology in order to get appropriate knowledge and skills required for my future profession.”

The author shares why they want to study biology, referring to the human body as the “perfect machine” and curious about how it performs each of its systems’ functions. The writer also mentions how biology is critical to their future profession. They aim to help people with their health problems and relay their desire to research the brain to find more data on it. 

“The study of biology owes great significance in human life, because man for its day-to-day requirements is dependent on plants and animals either directly or indirectly.”

Mol lists seven reasons why humans need biology in their daily lives. Her list includes health, diseases, agriculture, horticulture, food, animal breeding, and entertainment. She expounds on each point and how they affect a man during his time on Earth. She explains each relationship in a simple manner that’s easy to understand for the readers.

“Without biology, we would have no idea about an organism’s makeup, or the most basic unit of life, a cell… Biology influences me in many ways. Biology influences me by teaching me why to take care of the environment, why I am to take care of my body, and by giving me a better overall view of all scientific areas of study.”

In this short essay, the writer lists down reasons why biology is essential. These reasons include taking care of the environment, one’s body, and others. The author also expounds on their reasons by presenting facts supporting biology’s importance to the world and human lives.

“He told that the syllabus may be a good way to prepare for an exam but our knowledge should not be limited to any syllabus and the questions that were asked in the examination were related to the topic only. He told that if we try to know things in detail and understand them properly then the interest in the subject will develop, otherwise, students will not treat the subject as a subject of their choice. 

Bhattacharya shares his experience with a teacher with a unique teaching style. His Biology teacher from Class 7, before the era of the internet, don’t just carry one book to get all his lessons from. Instead, he has a notebook with the collated information from many books to teach his class. 

Bhattacharya’s teacher taught them things that were not in the curriculum, even if following the curriculum would give him higher points in his evaluation. He only wanted his students to learn more and share with them why learning differs from just knowing. 

Do you want to be sure you have an excellent essay? See our round-up of the best essay writing apps to help you check your output.

6 Prompts for Essays About Biology

You don’t have to be a biology student to write an essay about the subject. If you’re looking for easy prompts to write about, here are some to get you started:

If mitochondria are the powerhouse of the cell, who is the powerhouse of your classroom? Your home? Relate a biology topic to a similar structure in your life, then explain why you think they are the same. 

For instance, you can compare your mother to mitochondria which generate the energy needed to power a cell. The cell being you. You can say that she gives you energy every day by being there and supporting you in whatever way she can. This prompt bodes for a creative and intriguing essay.

Relay a lesson you learned from biology and how it perfectly explained something you were once hesitant about. Such as being insecure about your big ears – only to know from a biology trivia that ears never stop growing. You can then share how this help lessen your insecurity because you now know large ears are normal. 

Do you have a memory you won’t forget that happened during biology class? Narrate this story and explain why it’s something that left an impression on you. To give you an idea, you can talk about the first time you dissected an animal, where you first realized how complex organisms are and that they are made of many systems to function, no matter how small.

Gene action and heredity are evolving. If you have a genetic illness or know someone who has it, you can share your experience. Then explain what your genes have to do with the disease. Is it something you got from your parents? Did they inherit it from your grandparents? Finally, you can add what your parents’ and grandparents’ lives were like because of the disease.

Virology, another branch of biology, studies viruses and viral diseases. A recent example is the coronavirus pandemic, where more people realized the importance of knowing a virus’ origin, structure, and how they work. Write an essay where you explain how the pandemic operates, such as why people should wear masks, social distance, etc.

For this essay, you can write about how biology helps you care for your health. For example, you can include how biology helped doctors give you the appropriate diagnosis, how you had the opportunity to have the proper treatment, etc. 

If you want to write on a related topic, here are essay topics about nature you can consider for your next essay. 

Maria Caballero is a freelance writer who has been writing since high school. She believes that to be a writer doesn't only refer to excellent syntax and semantics but also knowing how to weave words together to communicate to any reader effectively.

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Defining Life: A Collection of Essays

Biologists have been unable to agree on a definition of the complex phenomenon known as “life.” In a special collection of essays in Astrobiology , a peer-reviewed journal from Mary Ann Liebert, Inc., leaders in the fields of philosophy, science, and molecular evolution present a variety of perspectives on defining life. The five essays in this collection are available for free download on the journal’s website.

Why is a definition of life so important yet so elusive? As David Deamer, Guest Editor and Research Professor of Biomolecular Engineering, University of California, Santa Cruz, writes in his Introduction, a definition is needed to help determine what is and is not life as scientists begin to develop artificial life forms in the laboratory and, in the future, dispatch exploratory rovers that investigate what appear to be life forms on other planets.

Mark Bedau, Reed College (Portland, OR) and the University of Southern Denmark (Odense), relies on the Program-Metabolism-Container ( PMC ) model to define minimal chemical life. He supports his belief that this integrated triad of chemical systems is all that is needed for a living organism to maintain its existence, grow, reproduce, and evolve, in the essay entitled, “An Aristotelian Account of Minimal Chemical Life.”

Antonio Lazcano, National Autonomous University of Mexico, and colleagues present an historical perspective of the many definitions of life put forth over the years and why they have been unsatisfactory, in the essay, “The Definition of Life: A Brief History of an Elusive Scientific Endeavor.”

Steven Benner, Foundation for Applied Molecular Evolution and The Westheimer Institute for Science and Technology (Gainesville, FL), explores the various definitions of life popular in the astrobiology community and how each is connected to a “theory of life.” In the essay “Defining Life,” Benner describes how chemical structures capable of Darwinian evolution might be useful as universal biosignatures.

Finally, an essay adapted from the writings of deceased Ukranian scientist Sergey Tsokolov asserts that feedback loops should be an essential component of any definition of life. Life could not exist in the absence of negative feedback, concludes Tsokolov in the essay “A Theory of Circular Organization and Negative Feedback: Defining Life in a Cybernetic Context.”

David Deamer commented, “These essays represent a remarkable effort on the part of the authors. We asked them to address a question that has challenged some of the great minds in biology, including Schrödinger himself, who initiated the discussion in 1944 with his book entitled “What Is Life?” Our authors rose to the challenge, and their ideas and perspectives are genuinely new. It was a pleasure to work with them and help them wrestle with this difficult and complex problem.” Deamer is the new Senior Editor in charge of essays on timely topics for Astrobiology.

Essay on Life for Students and Children

500+ words essay on life.

First of all, Life refers to an aspect of existence. This aspect processes acts, evaluates, and evolves through growth. Life is what distinguishes humans from inorganic matter. Some individuals certainly enjoy free will in Life. Others like slaves and prisoners don’t have that privilege. However, Life isn’t just about living independently in society. It is certainly much more than that. Hence, quality of Life carries huge importance. Above all, the ultimate purpose should be to live a meaningful life. A meaningful life is one which allows us to connect with our deeper self.

Why is Life Important?

One important aspect of Life is that it keeps going forward. This means nothing is permanent. Hence, there should be a reason to stay in dejection. A happy occasion will come to pass, just like a sad one. Above all, one must be optimistic no matter how bad things get. This is because nothing will stay forever. Every situation, occasion, and event shall pass. This is certainly a beauty of Life.

Many people become very sad because of failures . However, these people certainly fail to see the bright side. The bright side is that there is a reason for every failure. Therefore, every failure teaches us a valuable lesson. This means every failure builds experience. This experience is what improves the skills and efficiency of humans.

Probably a huge number of individuals complain that Life is a pain. Many people believe that the word pain is a synonym for Life. However, it is pain that makes us stronger. Pain is certainly an excellent way of increasing mental resilience. Above all, pain enriches the mind.

The uncertainty of death is what makes life so precious. No one knows the hour of one’s death. This probably is the most important reason to live life to the fullest. Staying in depression or being a workaholic is an utter wastage of Life. One must certainly enjoy the beautiful blessings of Life before death overtakes.

Get the huge list of more than 500 Essay Topics and Ideas

How to Improve Quality of Life?

Most noteworthy, optimism is the ultimate way of enriching life. Optimism increases job performance, self-confidence, creativity, and skills. An optimistic person certainly can overcome huge hurdles.

Meditation is another useful way of improving Life quality. Meditation probably allows a person to dwell upon his past. This way one can avoid past mistakes. It also gives peace of mind to an individual. Furthermore, meditation reduces stress and tension.

Pursuing a hobby is a perfect way to bring meaning to life. Without a passion or interest, an individual’s life would probably be dull. Following a hobby certainly brings new energy to life. It provides new hope to live and experience Life.

In conclusion, Life is not something that one should take for granted. It’s certainly a shame to see individuals waste away their lives. We should be very thankful for experiencing our lives. Above all, everyone should try to make their life more meaningful.

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AlphaFold 3 predicts the structure and interactions of all of life’s molecules

May 08, 2024

[[read-time]] min read

Introducing AlphaFold 3, a new AI model developed by Google DeepMind and Isomorphic Labs. By accurately predicting the structure of proteins, DNA, RNA, ligands and more, and how they interact, we hope it will transform our understanding of the biological world and drug discovery.

Inside every plant, animal and human cell are billions of molecular machines. They’re made up of proteins, DNA and other molecules, but no single piece works on its own. Only by seeing how they interact together, across millions of types of combinations, can we start to truly understand life’s processes.

In a paper published in Nature , we introduce AlphaFold 3, a revolutionary model that can predict the structure and interactions of all life’s molecules with unprecedented accuracy. For the interactions of proteins with other molecule types we see at least a 50% improvement compared with existing prediction methods, and for some important categories of interaction we have doubled prediction accuracy.

We hope AlphaFold 3 will help transform our understanding of the biological world and drug discovery. Scientists can access the majority of its capabilities, for free, through our newly launched AlphaFold Server , an easy-to-use research tool. To build on AlphaFold 3’s potential for drug design, Isomorphic Labs is already collaborating with pharmaceutical companies to apply it to real-world drug design challenges and, ultimately, develop new life-changing treatments for patients.

Our new model builds on the foundations of AlphaFold 2, which in 2020 made a fundamental breakthrough in protein structure prediction . So far, millions of researchers globally have used AlphaFold 2 to make discoveries in areas including malaria vaccines, cancer treatments and enzyme design. AlphaFold has been cited more than 20,000 times and its scientific impact recognized through many prizes, most recently the Breakthrough Prize in Life Sciences . AlphaFold 3 takes us beyond proteins to a broad spectrum of biomolecules. This leap could unlock more transformative science, from developing biorenewable materials and more resilient crops, to accelerating drug design and genomics research.

7PNM - Spike protein of a common cold virus (Coronavirus OC43): AlphaFold 3’s structural prediction for a spike protein (blue) of a cold virus as it interacts with antibodies (turquoise) and simple sugars (yellow), accurately matches the true structure (gray). The animation shows the protein interacting with an antibody, then a sugar. Advancing our knowledge of such immune-system processes helps better understand coronaviruses, including COVID-19, raising possibilities for improved treatments.

How AlphaFold 3 reveals life’s molecules

Given an input list of molecules, AlphaFold 3 generates their joint 3D structure, revealing how they all fit together. It models large biomolecules such as proteins, DNA and RNA, as well as small molecules, also known as ligands — a category encompassing many drugs. Furthermore, AlphaFold 3 can model chemical modifications to these molecules which control the healthy functioning of cells, that when disrupted can lead to disease.

AlphaFold 3’s capabilities come from its next-generation architecture and training that now covers all of life’s molecules. At the core of the model is an improved version of our Evoformer module — a deep learning architecture that underpinned AlphaFold 2’s incredible performance. After processing the inputs, AlphaFold 3 assembles its predictions using a diffusion network, akin to those found in AI image generators. The diffusion process starts with a cloud of atoms, and over many steps converges on its final, most accurate molecular structure.

AlphaFold 3’s predictions of molecular interactions surpass the accuracy of all existing systems. As a single model that computes entire molecular complexes in a holistic way, it’s uniquely able to unify scientific insights.

7R6R - DNA binding protein: AlphaFold 3’s prediction for a molecular complex featuring a protein (blue) bound to a double helix of DNA (pink) is a near-perfect match to the true molecular structure discovered through painstaking experiments (gray).

Leading drug discovery at Isomorphic Labs

AlphaFold 3 creates capabilities for drug design with predictions for molecules commonly used in drugs, such as ligands and antibodies, that bind to proteins to change how they interact in human health and disease.

AlphaFold 3 achieves unprecedented accuracy in predicting drug-like interactions, including the binding of proteins with ligands and antibodies with their target proteins. AlphaFold 3 is 50% more accurate than the best traditional methods on the PoseBusters benchmark without needing the input of any structural information, making AlphaFold 3 the first AI system to surpass physics-based tools for biomolecular structure prediction. The ability to predict antibody-protein binding is critical to understanding aspects of the human immune response and the design of new antibodies — a growing class of therapeutics.

Using AlphaFold 3 in combination with a complementary suite of in-house AI models, Isomorphic Labs is working on drug design for internal projects as well as with pharmaceutical partners. Isomorphic Labs is using AlphaFold 3 to accelerate and improve the success of drug design — by helping understand how to approach new disease targets, and developing novel ways to pursue existing ones that were previously out of reach.

AlphaFold Server: A free and easy-to-use research tool

8AW3 - RNA modifying protein: AlphaFold 3’s prediction for a molecular complex featuring a protein (blue), a strand of RNA (purple), and two ions (yellow) closely matches the true structure (gray). This complex is involved with the creation of other proteins — a cellular process fundamental to life and health.

Google DeepMind’s newly launched AlphaFold Server is the most accurate tool in the world for predicting how proteins interact with other molecules throughout the cell. It is a free platform that scientists around the world can use for non-commercial research. With just a few clicks, biologists can harness the power of AlphaFold 3 to model structures composed of proteins, DNA, RNA and a selection of ligands, ions and chemical modifications.

AlphaFold Server helps scientists make novel hypotheses to test in the lab, speeding up workflows and enabling further innovation. Our platform gives researchers an accessible way to generate predictions, regardless of their access to computational resources or their expertise in machine learning.

Experimental protein-structure prediction can take about the length of a PhD and cost hundreds of thousands of dollars. Our previous model, AlphaFold 2, has been used to predict hundreds of millions of structures, which would have taken hundreds of millions of researcher-years at the current rate of experimental structural biology.

Sharing the power of AlphaFold 3 responsibly

With each AlphaFold release, we’ve sought to understand the broad impact of the technology , working together with the research and safety community. We take a science-led approach and have conducted extensive assessments to mitigate potential risks and share the widespread benefits to biology and humanity.

Building on the external consultations we carried out for AlphaFold 2, we’ve now engaged with more than 50 domain experts, in addition to specialist third parties, across biosecurity, research and industry, to understand the capabilities of successive AlphaFold models and any potential risks. We also participated in community-wide forums and discussions ahead of AlphaFold 3’s launch.

AlphaFold Server reflects our ongoing commitment to share the benefits of AlphaFold, including our free database of 200 million protein structures. We’ll also be expanding our free AlphaFold education online course with EMBL-EBI and partnerships with organizations in the Global South to equip scientists with the tools they need to accelerate adoption and research, including on underfunded areas such as neglected diseases and food security. We’ll continue to work with the scientific community and policy makers to develop and deploy AI technologies responsibly.

Opening up the future of AI-powered cell biology

7BBV - Enzyme: AlphaFold 3’s prediction for a molecular complex featuring an enzyme protein (blue), an ion (yellow sphere) and simple sugars (yellow), along with the true structure (gray). This enzyme is found in a soil-borne fungus (Verticillium dahliae) that damages a wide range of plants. Insights into how this enzyme interacts with plant cells could help researchers develop healthier, more resilient crops.

AlphaFold 3 brings the biological world into high definition. It allows scientists to see cellular systems in all their complexity, across structures, interactions and modifications. This new window on the molecules of life reveals how they’re all connected and helps understand how those connections affect biological functions — such as the actions of drugs, the production of hormones and the health-preserving process of DNA repair.

The impacts of AlphaFold 3 and our free AlphaFold Server will be realized through how they empower scientists to accelerate discovery across open questions in biology and new lines of research. We’re just beginning to tap into AlphaFold 3’s potential and can’t wait to see what the future holds.

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Google DeepMind and Isomorphic Labs reveal AI able to predict large swathes of molecular biology

Alphabet’s Google DeepMind and its sister company Isomorphic Labs have created a new AI model that they say can help predict both the structure and interaction of most molecules involved in biological processes, including proteins, DNA, RNA, and some of chemicals used to create new medicines. The new model is a potentially giant leap for biological research. The companies are allowing researchers working on non-commerical projects to query the model for free through an internet-based interface.

Isomorphic Labs, which was spun out of Google DeepMind, has also begun using the system internally to speed its efforts to discover new drugs. The company currently has partnerships with Eli Lilly and Novartis aimed at developing multiple drugs, although the specifics of which diseases the companies are targeting has not been revealed. Proteins are the building blocks of life and their interactions with one another and with other molecules are the mechanism through which life’s processes happen. Being able to predict those interactions more accurately will help researchers advance science. by helping them understand the mechanism behind diseases, and, potentially, how to better treat and cure them. Called AlphaFold 3, the new AI software represents a major update and expansion of capabilities beyond Google DeepMind’s previous AlphaFold 2 system . Researchers from the companies published a paper on AlphaFold 3 today in the prestigious scientific journal Nature . Demis Hassabis, who serves as CEO of both Google DeepMind and Isomorphic, described the new model’s interaction predictions as “incredibly important for drug discovery.” John Jumper, the senior researcher who heads the protein structure team at Google DeepMind, described AlphaFold 3 as “an evolution of AlphaFold 2, but a really big one that opens up new avenues.” He also said he was excited to see what researchers would do with the new model, noting that AlphaFold 2 had already opened up new areas of biological research that he could never have imagined. AlphaFold 2 has been cited more than 20,000 times in other published scientific papers and has been used to work on drugs for malaria, cancer, and many other diseases.

AlphaFold 2 and 3

Debuted in late 2020, AlphaFold 2 solved a grand scientific challenge because it was able to accurately predict the structure of most proteins simply from their DNA sequence. The company later published the system’s predicted structures for all 200 million proteins with known DNA sequences and made them freely available to scientists in a massive database. Prior to this, only about 100,000 proteins had known structural information. Knowing the shape and structure of a protein is often a key part of understanding how it will function. But proteins do not work in isolation. And AlphaFold 2 was not designed to predict how proteins would interact with one another—although scientists soon found ways to modify AlphaFold 2 to make some of these predictions. Nor could AlphaFold 2 predict protein interactions with other kinds of molecules, such as DNA, RNA, ligands, and ions, that are found inside living things. It also could not predict the interaction of these other molecules with one another. AlphaFold 3 can. The system is not always accurate, but represents a major leap forward in performance. According to tests conducted by Google DeepMind and Isomorphic, AlphaFold 3 can accurately predict 76% of protein interactions with small molecules, compared to 52% for the previous best predictive software. It can predict 65% of DNA interactions compared to the next leading system, which only achieves 28%. And in protein to protein interactions, it can predict 62% accurately, more than doubling what AlphaFold 2 could do. Like AlphaFold 2, AlphaFold 3 also includes a confidence score alongside its predictions that give scientists some indication of whether they should trust the system’s output. This reduces the chance that the AI model will experience the sort of “hallucinations”—plausible but inaccurate outputs—that have plagued recent generative AI models. Jumper said that so far researchers have found these confidence scores to be highly correlated with whether the structural and interaction predictions are accurate. In other words, the system is not likely to be confidently wrong. There are a few classes of proteins where AlphaFold 3 is still not accurate. These include proteins that scientists consider “intrinsically disordered,” meaning they only assume a particular structure in the presence of another protein or molecule, perhaps changing their shape radically depending on circumstance, according to Max Jaderberg, the chief AI scientist at Isomorphic Labs.

Bioweapons worries

While many, including former Google DeepMind cofounder Mustafa Suleyman , who is now heading up a new consumer AI division at Microsoft , and Dario Amodei, the confounder and CEO of Google DeepMind rival Anthropic, have warned that rapid advances in AI may lead to the proliferation of bioweapons by radically lowering the knowledge barrier to creating deadly pathogens, Jumper said Google DeepMind and Isomorphic had consulted more than 50 experts in biosecurity, bioethics, and AI safety and concluded that the marginal risk AlphaFold 3 might present in terms of bioweapons creation was far outweighed by the system’s potential benefits to science, including advancing human understanding of disease and finding possible treatments.

The two companies are also only allowing access to the model through an internet service that allows outside researchers to prompt the system and receive a prediction, but does not give them access to the model itself or its underlying computer code. Unlike some efforts to create large language models (LLMs) for biology that can be prompted in natural language to produce a formula for a compound with particular properties, AlphaFold 3 still requires someone to have a fairly good understanding of biology to use it effectively. In addition, any suggested molecular structure it predicts would still need to be produced or isolated in a lab, a process that also requires relatively specialized knowledge. AlphaFold 3 uses a significantly different AI design than its predecessor AlphaFold 2. While both AI models are based around transformers, a kind of artificial neural network architecture pioneered by Google researchers in 2017, Jumper said the team working on the new system replaced entire “blocks” of the large transformer that powered AlphaFold 2.

AlphaFold 2 relied heavily on evolutionary information about the proteins for which it was trying to predict structures, while AlphaFold 3 leans on this evolutionary signal far less, using it only at the first step of its structure prediction. Instead, the new system devotes the majority of its components to working through the physical shape of the molecules it is making predictions about.

AlphaFold 3 also uses a diffusion model, similar to ones used for popular text-to-image generation models such as OpenAI’s DALL-E 3 or Midjourney, to learn how to puzzle out the precise atomic structures of molecules. Overall, despite covering far more substances than AlphaFold 2, AlphaFold 3 is a simpler design, with fewer separate components, than its predecessor.  

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Roger Corman: a career in pictures

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Best known for his low-budget Edgar Allan Poe adaptations, Corman also produced over 400 films and helped kickstart the careers of Jack Nicholson, Nicholas Roeg, Peter Fonda, James Cameron and Martin Scorsese

• News: Corman dies aged 98
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Greg Whitmore

Sun 12 May 2024 08.59 BST Last modified on Sun 12 May 2024 22.07 BST

Photograph: Hulton Archive/Getty Images

Day The World Ended, 1955

Photograph: Alamy

The Undead, 1957

Photograph: The Kobal Collection

Not Of This Earth and Attack Of The Crab Monsters, both 1957

Composite: Movie Poster Image Art/ Getty Images

Attack of the Crab Monsters, 1957

Teenage Doll, 1957

Photograph: Everett/REX Shutterstock

The Wasp Woman, 1959

Photograph: Moviestore/REX Shutterstock

The Fall of the House of Usher, 1960

The Little Shop of Horrors, 1960

The Pit and the Pendulum, 1961

X: The Man with the X-Ray Eyes, 1963

Photograph: Public Domain

Tomb of Ligeia, 1964

The Masque of the Red Death, 1964

Composite: BFI

The Wild Angels, 1966

Photograph: Ronald Grant Archive

The St. Valentine’s Day Massacre, 1967

Composite: REX Shutterstock/Alamy

The Trip, 1967

Photograph: Movie Poster Image Art/Getty Images

Bloody Mama, 1970

Composite: REX/Ronald Grant Archive

Photograph: Getty Images

Frankenstein Unbound, 1990

Composite: REX Shutterstock

Photograph: Michael Yada/Getty Images

Photograph: Victoria Will/Invision/AP

• Roger Corman
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• Science fiction and fantasy films
• Edgar Allan Poe

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Joseph Epstein, conservative provocateur, tells his life story in full

In two new books, the longtime essayist and culture warrior shows off his wry observations about himself and the world

Humorous, common-sensical, temperamentally conservative, Joseph Epstein may be the best familiar — that is casual, personal — essayist of the last half-century. Not, as he might point out, that there’s a lot of competition. Though occasionally a scourge of modern society’s errancies, Epstein sees himself as essentially a serious reader and “a hedonist of the intellect.” His writing is playful and bookish, the reflections of a wry observer alternately amused and appalled by the world’s never-ending carnival.

Now 87, Epstein has just published his autobiography, “ Never Say You’ve Had a Lucky Life: Especially if You’ve Had a Lucky Life ,” in tandem with “ Familiarity Breeds Content: New and Selected Essays .” This pair of books brings the Epstein oeuvre up to around 30 volumes of sophisticated literary entertainment. While there are some short-story collections (“The Goldin Boys,” “Fabulous Small Jews”), all the other books focus on writers, observations on American life, and topics as various as ambition, envy, snobbery, friendship, charm and gossip. For the record, let me add that I own 14 volumes of Epstein’s views and reviews and would like to own them all.

Little wonder, then, that Epstein’s idea of a good time is an afternoon spent hunched over Herodotus’s “Histories,” Marguerite Yourcenar’s “Memoirs of Hadrian” or almost anything by Henry James, with an occasional break to enjoy the latest issue of one of the magazines he subscribes to. In his younger days, there were as many as 25, and most of them probably featured Epstein’s literary journalism at one time or another. In the case of Commentary, he has been contributing pieces for more than 60 years.

As Epstein tells it, no one would have predicted this sort of intellectual life for a kid from Chicago whose main interests while growing up were sports, hanging out, smoking Lucky Strikes and sex. A lackadaisical C student, Myron Joseph Epstein placed 169th in a high school graduating class of 213. Still, he did go on to college — the University of Illinois at Urbana-Champaign — because that’s what was expected of a son from an upper-middle-class Jewish family. But Urbana-Champaign wasn’t a good fit for a jokester and slacker: As he points out, the president of his college fraternity “had all the playfulness of a member of the president’s Council of Economic Advisers.” No matter. Caught peddling stolen copies of an upcoming accounting exam for $5 a pop, Epstein was summarily expelled.

Fortunately, our lad had already applied for a transfer to the University of Chicago, to which he was admitted the next fall. Given his record, this shows a surprising laxity of standards by that distinguished institution, but for Epstein the move was life-changing. In short order, he underwent a spiritual conversion from good ol’ boy to European intellectual in the making. In the years to come, he would count the novelist Saul Bellow and the sociologist Edward Shils among his close friends, edit the American Scholar, and teach at Northwestern University. His students, he recalls, were “good at school, a skill without any necessary carry-over, like being good at pole-vaulting or playing the harmonica.”

Note the edge to that remark. While “Never Say You’ve Had a Lucky Life” is nostalgia-laden, there’s a hard nut at its center. Epstein feels utter contempt for our nation’s “radical change from a traditionally moral culture to a therapeutic one.” As he explains: “Our parents’ culture and that which came long before them was about the formation of character; the therapeutic culture was about achieving happiness. The former was about courage and honor, the latter about self-esteem and freedom from stress.” This view of America’s current ethos may come across as curmudgeonly and reductionist, but many readers — whatever their political and cultural leanings — would agree with it. Still, such comments have sometimes made their author the focus of nearly histrionic vilification.

Throughout his autobiography, this lifelong Chicagoan seems able to remember the full names of everyone he’s ever met, which suggests Epstein started keeping a journal at an early age. He forthrightly despises several older writers rather similar to himself, calling Clifton Fadiman, author of “The Lifetime Reading Plan,” pretentious, then quite cruelly comparing Mortimer J. Adler, general editor of the “Great Books of the Western World” series, with Sir William Haley, one of those deft, widely read English journalists who make all Americans feel provincial. To Epstein, “no two men were more unalike; Sir William, modest, suave, intellectually sophisticated; Mortimer vain, coarse, intellectually crude.” In effect, Fadiman and Adler are both presented as cultural snake-oil salesmen. Of course, both authors were popularizers and adept at marketing their work, but helping to enrich the intellectual lives of ordinary people doesn’t strike me as an ignoble purpose.

In his own work, Epstein regularly employs humor, bits of slang or wordplay, and brief anecdotes to keep his readers smiling. For instance, in a chapter about an editorial stint at the Encyclopaedia Britannica, Epstein relates this story about a colleague named Martin Self:

“During those days, when anti-Vietnam War protests were rife, a young woman in the office wearing a protester’s black armband, asked Martin if he were going to that afternoon’s protest march. ‘No, Naomi,’ he said, ‘afternoons such as this I generally spend at the graveside of George Santayana.’”

Learned wit, no doubt, but everything — syntax, diction, the choice of the philosopher Santayana for reverence — is just perfect.

But Epstein can be earthier, too. Another colleague “was a skirt-chaser extraordinaire," a man "you would not feel safe leaving alone with your great-grandmother.” And of himself, he declares: “I don’t for a moment wish to give the impression that I live unrelievedly on the highbrow level of culture. I live there with a great deal of relief.”

In his many essays, including the sampling in “Familiarity Breeds Content,” Epstein is also markedly “quotacious,” often citing passages from his wide reading to add authority to an argument or simply to share his pleasure in a well-turned observation. Oddly enough, such borrowed finery is largely absent from “Never Say You’ve Had a Happy Life.” One partial exception might be the unpronounceable adjective “immitigable,” which appears all too often. It means unable to be mitigated or softened, and Epstein almost certainly stole it from his friend Shils, who was fond of the word.

Despite his autobiography’s jaunty title, Epstein has seen his share of trouble. As a young man working for an anti-poverty program in Little Rock, he married a waitress after she became pregnant with his child. When they separated a decade later, he found himself with four sons to care for — two from her previous marriage, two from theirs. Burt, the youngest, lost an eye in an accident while a toddler, couldn’t keep a job, fathered a child out of wedlock and eventually died of an opioid overdose at 28. Initially hesitant, Epstein came to adore Burt’s daughter, Annabelle, as did his second wife, Barbara, whom he married when they were both just past 40.

Some pages of “Never Say You’ve Had a Lucky Life” will be familiar to inveterate readers of Epstein’s literary journalism, all of which carries a strong first-person vibe. Not surprisingly, however, the recycled anecdotage feels less sharp or witty the second time around. But overall, this look back over a long life is consistently entertaining, certainly more page-turner than page-stopper. To enjoy Epstein at his very best, though, you should seek out his earlier essay collections such as “The Middle of My Tether,” “Partial Payments” and “A Line Out for a Walk.” Whether he writes about napping or name-dropping or a neglected writer such as Somerset Maugham, his real subject is always, at heart, the wonder and strangeness of human nature.

Never Say You’ve Had a Lucky Life

Especially if You’ve Had a Lucky Life

By Joseph Epstein

Free Press. 304 pp. $29.99

Familiarity Breeds Content

New and Selected Essays

Simon & Schuster. 464 pp. $20.99

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