This note discuses the understanding of 'life'.


Life is speculation. Living systems engage in continuing hypothesis testing. They try out all solutions that are possible within the path-dependent search space. Living systems attempt billions simultaneous field tests and response tells them what works.

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

Life as an expression of motion or of energy dissipation. In this perspective, there is no hard ontological boundary between life and non-life as the universe consists of processes and complexification occurs in all 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 these spaces and fills them with innovations (species, behaviours, etc.).

New inventions exist along with and often depend on the previous ones (for new species and ecosystems, the existing ones are the environment, the resrources, places, etc.). Pre-existing form are the environment for the new forms from the beginning and new niches depend on the old patterns.

The layered approach to innovation is not optimal. The reuse and redeployment of existing blocks for new function has significant overheads and inefficiencies, sometime contradictions and negative consequences. Repetition of functions and the retention of the lower order functions can be useful for resilience in the face of change.

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

for the 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 the definition of life based on its actions.

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


  • 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 an example of 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 list of essential properties of life and is comprehensive.

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

Life may be described as “a flow of energy, matter and information” (Baltscheffsky, 1997; source Popa 2004). Strength: It includes flow of information. Life is an expected, collectively self-organized property of catalytic polymers (Kauffmann, 1993; source Popa 2004). Strength: It includes catalysis and selforganization; 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.

Life is defined as “a material system that can acquire, store, process, and use information to organize its activities” (Dyson, 2000; source Popa 2004). 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: A focus 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 metabolizing material informational system with the ability of self-reproduction with changes (evolution), which requires energy and suitable environment (Trifonov 2011). This is a composite definition of nine groups of defining terms that were used in 123 definitions of life. Strength: It is comprehensive.

Life is a chemical system capable of transferring its molecular information independently (selfreproduction) and also capable of making some accidental errors to 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.

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

Life is a new quality brought upon an organic chemical system by a dialectic change resulting from an increase in quantity of complexity of the system. 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 combined have a potential to metabolize, reproduce, interact with the environment, including other life forms, and are the subject of natural selection (Kolb and Liesch 2008). Strength: It includes life forms; comprehensive. We propose that 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’s 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 to reproduce its mutation must almost inevitably evolve in directions that will 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 a system is discovered to be autopoietic, that system is defined 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 and, especially, to speculative design and Speculation

Living System

As distinct from an organism, an individual, etc.

"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.


The notion of death is only applicable to multicellular organisms. Viruses lack individuality. Microbes can reproduce by division.

Death for reproducing individuals is functionally useful as it frees space by removing individuals who cannot reproduce.

The notion of death is also not applicable to the totality of life, at least not in the known conditions, or at least this is not the direction of life as known.

Value of Life

In many domains, there is a tendency to celebrate life. However, life - and its method in particular - are not positive or negative.

Indeed, there are objections to the proposals to seed life on other planets on the basis that the life on Earth leads to huge amounts of suffering.

O’Brien, Gary David. ‘Directed Panspermia, Wild Animal Suffering, and the Ethics of World-Creation’. Journal of Applied Philosophy, 2021.

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.

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,

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 (death, illness, suffering, etc.), 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.


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


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. the 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.


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.