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Life

This note examines how we understand life.

Is “life” an ontological category or an interpretative construct?

Fields, Chris, and Michael Levin. “Life, Its Origin, and Its Distribution: A Perspective from the Conway-Kochen Theorem and the Free Energy Principle.” Communicative & Integrative Biology 18, no. 1 (2025): 2466017. https://doi.org/10/g9k5k6.

Definition

Differentiate between definitions of life based on its properties and Life understood as a clade of all living things (cf. Gaia). The latter includes, for example, all current life on Earth.1 Other forms of life on Earth likely existed but are now extinct.

Hug, Laura A., Brett J. Baker, Karthik Anantharaman, Christopher T. Brown, Alexander J. Probst, Cindy J. Castelle, Cristina N. Butterfield, et al. “A New View of the Tree of Life.” Nature Microbiology 1, no. 5 (2016): 16048. https://doi.org/10.1038/nmicrobiol.2016.48.

Life is speculation. Living systems engage in continuous hypothesis testing. They try solutions that remain possible within a path-dependent search space. They run billions of simultaneous field tests, and the results show what works.

Margulis, Lynn, and Dorion Sagan. What Is Life? Berkeley: University of California Press, 2000.

Life can also be understood as an expression of motion or energy dissipation. From this perspective, no hard ontological boundary separates life from non-life because the universe consists of processes, and complexification occurs across many kinds of systems.

Kolb, Vera M., ed. Handbook of Astrobiology. Boca Raton: CRC Press, 2019.

Life is a process of matter differentiation. It creates more complex worlds. Life explores 'spaces of possibilities', creates habitable niches within those spaces, and fills them with innovations such as species and behaviours.

New inventions coexist with, and often depend on, earlier ones. For new species and ecosystems, existing species and ecosystems provide the environment, resources, and places in which novelty emerges. Pre-existing forms shape the conditions for new forms from the outset, and new niches depend on older patterns.

This layered approach to innovation is not optimal. The reuse and redeployment of existing blocks for new functions creates overheads, inefficiencies, contradictions, and negative consequences. However, repeated functions and retained lower-order functions can support resilience in changing conditions.

Chernyshenko, Serge V. “Phenomenon of Life: General Aspects.” In Encyclopedia of Ecology, edited by Brian Fath, 2nd ed. 2008. Reprint, Oxford: Elsevier, 2019.

For an overview and definitions, see:

Ward, Peter D., and Joseph L. Kirschvink. A New History of Life: The Radical New Discoveries About the Origins and Evolution of Life on Earth. New York: Bloomsbury Press, 2015.

For a definition of life based on its actions, see:

Davies, Paul. The Fifth Miracle: The Search For The Origin And Meaning Of Life. New York: Simon & Schuster, 1998.

Life:

  • metabolises
  • has complexity and organisation
  • reproduces
  • develops
  • evolves
  • is autonomous

NASA (via Sagan):

"Life is a chemical system capable of Darwinian evolution."

"Seeing life as an evolving set of processes, including metabolism, life cycles and symbioses, is a way of seeing life wherein the organism, the cell and the genome are in flux and whose component parts are entities that are made through the concrescences of numerous processes."

Gilbert, Sarah R., and Scott F. Gilbert. ‘Process Epistemologies for the Careful Interplay of Art and Biology: An Afterword’. In Drawing Processes of Life: Molecules, Cells, Organisms, edited by Gemma Anderson and John Dupré, 295–320. Bristol: Intellect, 2023.

Examples of Definitions

Life 1a: the quality that distinguishes a vital and functional being from a dead body; b: a principle or force that is considered to underlie the distinctive quality of animate beings (compare vitalism); c: an organismic state characterized by capacity for metabolism, growth, reaction to stimuli, and reproduction … 5 a: the period from birth to death (Merriam-Webster’s Collegiate® Dictionary, Tenth Edition, 1993). This is a lexical definition of life.

Life as a system capable of (1) self-organization, (2) self-replication, (3) evolution through mutation, (4) metabolism, and (5) concentrative encapsulation (Arrhenius, 2002; source Popa 2004). Strength: It gives a comprehensive list of essential properties.

Life is the process of existence of open non-equilibrium complete systems, which are composed of carbon-based polymers and can self-reproduce and evolve on the basis of template synthesis of their polymer components (Altstein, 2002; source Popa 2004). Strength: It is specific about thermodynamic and chemical requirements.

Baltscheffsky (1997; source Popa 2004) describes life as “a flow of energy, matter and information.” Strength: It includes the flow of information. Kauffmann (1993; source Popa 2004) treats life as an expected, collectively self-organized property of catalytic polymers. Strength: It includes catalysis and self-organization; life is expected.

Life is a self-sustained chemical system capable of undergoing Darwinian evolution (NASA’s working definition of life; Joyce 1994, 2002; source Popa 2004). Strength: It includes Darwinian evolution and self-sustainability as criteria for life.

Dyson (2000; source Popa 2004) defines life as “a material system that can acquire, store, process, and use information to organize its activities.” Strength: It includes information. Any living system must comprise four distinct functions: (1) increase of complexity; (2) directing the trends of increased complexity; (3) preserving complexity; and (4) recruiting and extracting the free energy needed to drive the three preceding motions (Anbar, 2002; source Popa 2004). Strength: It focuses on complexity.

Any system capable of replication and mutation is alive (Oparin, 1961; source Popa 2004). Strength: It gives key properties of life.

Life is self-reproduction with variations (Trifonov 2011). Strength: This is a minimal definition of life. It is like Oparin’s definition (Oparin 1961; source Popa 2004).

Life is a metabolizing material informational system with the ability of self-reproduction with changes (evolution), which requires energy and a suitable environment (Trifonov 2011). This is a composite definition of nine groups of defining terms used in 123 definitions of life. Strength: It is comprehensive.

Life is a chemical system capable of transferring its molecular information independently (self-reproduction) and also capable of making some accidental errors that allow the system to evolve (evolution) (Brack, 2002; source Popa 2004). Strength: Chemical accidental errors enable evolution.

Life is synonymous with the possession of genetic properties, that is, the capacities for self-replication and mutation (Horowitz, 2002; source Popa 2004). Strength: A focus on key properties of life.

Friedman (2002, paraphrasing Theodosius Dobzhansky; source Popa 2004) suggests that life is what the scientific establishment, probably after some healthy disagreement, will accept as life. Strength: It reveals a drawback of stipulatory definitions, which can change.

Life is a new quality brought to an organic chemical system by a dialectic change resulting from an increase in the quantity of the system's complexity. This new quality is characterized by the ability of temporal self-maintenance and self-preservation (Kolb, 2002; source Popa 2004). Strength: It includes the origin of life as the result of abiotic-to-biotic transition via a dialectic change, and as such is expected.

Life is a chemical phenomenon that occurs in space and time as a succession of life forms that, together, have the potential to metabolize, reproduce, interact with the environment, including other life forms, and undergo natural selection (Kolb and Liesch 2008). Strength: It includes life forms; comprehensive. We propose that the life of an organism is the sum of its life forms over a period of time. We set the integral of time from the birth of the organism to its death (Kolb 2010). Strength: It includes life forms of an organism.

It is alive if it can die (Lauterbur, 2002; source Popa 2004). Strength: It includes death as a criterion for life.

No physiology is held to be scientific if it does not consider death an essential factor of life. Life means dying (Engels ca. 1880; source Popa 2004). Strength: It includes death in defining life.

Life (L) is a total sum (Σ) of all acts of communication (C) executed by a sender-receiver at all its levels of compartmental organization. Thus L = ΣC (De Loof 2015). Strength: It includes communication as a criterion for life.

Life is synonymous with the possession of genetic properties. Any system with the capacity to mutate freely and reproduce its mutation must almost inevitably evolve in directions that ensure its preservation. Given sufficient time, the system will acquire the complexity, variety, and purposefulness that we recognize as alive (Horowitz, 1986; source Popa 2004). Strength: It gives the essential properties of life, and it includes purposefulness.

The characteristics that distinguish most living things from non-living things include a precise kind of organization; a variety of chemical reactions that we term metabolism; the ability to maintain an appropriate internal environment, even when the external environment changes (a process referred to as homeostasis); and movement, responsiveness, growth, reproduction, and adaptation to environmental change (Vilee et al., 1989; source Popa 2004). Strength: It gives a detailed list of the essential properties; it includes homeostasis.

Any definition of life that is useful must be measurable. We must define life in terms that can be turned into measurables and then turn these into a strategy that can be used to search for life. So, what are these? (1) structures; (2) chemistry; (3) replication with fidelity; and (4) evolution (Nealson, 2002; source Popa 2004). Strength: A focus on measurables to define life.

Life is a metabolic network within a boundary (Maturana and Varela, 1980; reformulated by Luisi, 1993; source Popa 2004). All that is living must be based on autopoiesis, and if researchers discover that a system is autopoietic, that system counts as living; that is, it must correspond to the definition of minimal life (Maturana and Varela 1980). Strength: It gives autopoiesis as a criterion for life.

A living system is a system capable of self-production and self-maintenance through a regenerative network of processes that takes place within a boundary of its own making and regenerates itself through cognitive or adaptive interactions with the medium (Damiano and Luisi 2010; this is a reformulation of the original Maturana and Varela definition of living; Maturana and Varela 1980). Strength: Focus on autopoiesis.

Life is a historical process “as the mode of existence of ribosome encoding organisms (cells) and capsid encoding organisms (viruses) and their ancestors” (Forterre 2010). Strength: This definition includes viruses.

Popa, Radu. Between Necessity and Probability: Searching for the Definition and Origin of Life. Berlin: Springer, 2004.

Consider the link to Design, especially speculative design and Speculation.

Living System

This category is distinct from an organism or an individual.

"A living system is:

  • A a self-organized non-equilibrium system such that
  • B its processes are governed by a program which is stored symbolically and
  • C it can reproduce itself, including the program."

Smolin, Lee. The Life of the Cosmos. New York: Oxford University Press, 1997.

"a physical system is alive if it is capable of transforming a flux of external matter and energy into an internal flux of self-maintenance and self-reproduction." Maturana and Varela via

Barbieri, Marcello. The Organic Codes: An Introduction to Semantic Biology. Cambridge: Cambridge University Press, 2003.

Death

The notion of death applies most clearly to multicellular organisms. Viruses lack individuality, and microbes can reproduce by division.

For reproducing individuals, death can be functionally useful because it frees space by removing individuals that can no longer reproduce.

Death also does not apply straightforwardly to the totality of life, at least under known conditions. Life as a whole does not appear to move in that direction.

Value of Life

Many domains tend to celebrate life. However, life, and its method in particular, are not intrinsically positive or negative.

Indeed, some object to proposals to seed life on other planets because life on Earth produces large amounts of suffering.

O’Brien, Gary David. ‘Directed Panspermia, Wild Animal Suffering, and the Ethics of World-Creation’. Journal of Applied Philosophy, 2021. https://doi.org/10/gnv2dq.

The idyllic view of life is inaccurate.

Animals routinely suffer many harms, cf. Nature:

  • predation and parasitism
  • intraspecific competition
  • sexual conflict
  • disease
  • extreme weather conditions
  • hunger and thirst
  • physical injuries
  • accidents

For a brief overview of wild animal suffering, see: The situation of animals in the wild — Animal Ethics

On animal suffering in nature:

Tomasik, Brian. ‘The Importance of Wild-Animal Suffering Wild Animal Suffering and Intervention in Nature: Studies and Research Contributions’. Relations: Beyond Anthropocentrism 3 (2015): 133–52. https://doi.org/10/gf3nx2.

Also see this podcast: Knowing Animals: Episode 173: Directed panspermia with Gary O'Brien

Oscar Horta, ‘Debunking the Idyllic View of Natural Processes: Population Dynamics and Suffering in the Wild’, Télos, 2010, 73–88.

On reproductive strategies that expect the death of multiple offspring:

Kyle Johannsen, ‘Animal Rights and the Problem of r-Strategists’, Ethical Theory and Moral Practice 20, no. 2 (2017): 333–45, https://doi.org/10/gnv2hf.

Andrew Chignell, Terence Cuneo, and Matthew C. Halteman, eds., ‘The Moral Problem of Predation’, in Philosophy Comes to Dinner: Arguments on the Ethics of Eating (New York: Routledge, 2016), 268–93.

All life is precarious because it is exposed to death, illness, suffering, and related conditions, cf. Butler, Chan.

Butler, Judith. Frames of War: When Is Life Grievable? London: Verso, 2009.

Biological Systems

Chernyshenko, Serge V. “Phenomenon of Life: General Aspects.” In Encyclopedia of Ecology, edited by Brian Fath, 2nd ed. 2008. Reprint, Oxford: Elsevier, 2019.

Enactive Conception of Life

Thompson, Evan. Mind in Life: Biology, Phenomenology, and the Sciences of Mind. Cambridge, MA: Belknap Press of Harvard University Press, 2007.

Di Paolo, Ezequiel A., Thomas Buhrmann, and Xabier E. Barandiaran. Sensorimotor Life: An Enactive Proposal. Oxford: Oxford University Press, 2017.

Abilities

Memory is one way life organises for the future, anticipates events and consequences, and prepares actions.

Divisions

Sympoietic and autopoietic: organisms or other boundaries.

Dempster, Beth. ‘Sympoietic and Autopoietic Systems: A New Distinction for Self-Organizing Systems’. In Proceedings of the World Congress of the Systems Sciences and ISSS 2000, edited by Jennifer Wilby and Janet K. Allen, 1–15. Toronto: ISSS, 2000.

Cf. horizontal gene transfer.

Quammen, David. The Tangled Tree: A Radical New History of Life. New York: Simon & Schuster, 2018.

History of Life

Godfrey-Smith, Peter. Metazoa: Animal Life and the Birth of the Mind. New York: Farrar, Straus and Giroux, 2020.

Shubin, Neil. Your Inner Fish: A Journey Into the 3.5-Billion-Year History of the Human Body. Revised. New York: Vintage, 2009.

References

Seifert, Josef. What Is Life? The Originality, Irreducibility, and Value of Life. Boston: Brill, 1997.

Deamer, David W. Origin of Life: What Everyone Needs to Know. What Everyone Needs to Know. New York: Oxford University Press, 2020.

Footnotes

  1. Lenton, Timothy M., Sébastien Dutreuil, and Bruno Latour. “Life on Earth Is Hard to Spot.” The Anthropocene Review 7, no. 3 (2020): 248–72. https://doi.org/10.1177/2053019620918939.˄

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