Meeting 2.1 – Attempts to Define Life

The science and religion reading group at MIT met on 12 February 2014.


Weber, Bruce, “Life”, The Stanford Encyclopedia of Philosophy (Winter 2011 Edition), Edward N. Zalta (ed.)

Definitions:  Lucas Mix presented a number of potential definitions for life.

There is currently no consensus on the definition of life.  Neither is their consensus on the need for such a definition.

Pornography Definition:  I can’t say what it is, but I know it when I see it.

Syndrome Definition:  This definition presents a list of traits or symptoms of life often without formal differentiae or causes.  Symptoms often include reproduction, homeostasis, growth, death, movement, bounding, and interaction with environment.

Entelechism (Aristotle): Life as reified, end-oriented project.

Vitalism, often attributed to Aristotle, sees life as a “fundamental, irreducible property of nature” (Weber).

Mechanism (Descartes): Human life as agents with willful minds; animals and plants as mechanistic, deterministic, and powered by natural forces.

By and large, the mechanical ontology, reducing all observed phenomena to regular interactions between particles and universal forces took over physics and chemistry in the 17th century, but mechanist biology was not popular until after Darwin and Mendel. Vitalist mechanisms were popular between the mid 19th and mid 20th centuries.  Physicalist mechanisms have become popular subsequently.  In the same period, there was a push for a dynamic (process oriented) definition, rather than a static (component oriented) one.

Adaptation (Sagan): Life is “a self-sustaining chemical system capable of Darwinian evolution” (Joyce).

Negentropy (Schroedinger): Life maintains disequilibrium with the environment and delays decay toward greater entropy.  The related concepts of Complexity, Information Content, and Feedback Loop have also been proposed.


Are there options not listed here that we should consider?

Two philosophers were suggested:

Mark Johnston (Princeton) has a modern theory of hylomorphism.

Peter van Inwagen (Notre Dame) has a theory of material entities.


Is a definition of life necessary for biology?  For some subset of biology?

The definition of life appears to be necessary for the search for life beyond earth (astrobiology/exobiology) and origin of life studies.  We agreed that there were areas within biology that had operational definitions of life but no over-all or even sub-field-wide consensus.

Is life a natural category?

Compositional problems appear to be key.  What are we lumping together or splitting apart to create a definition of life? Is it about the holistic integrity of an organism, a dynamic property of a chemical system, or something else.

Is “natural categories” a useful or meaningful term? We were divided. Is it meant to represent some fundamental ordering of the universe as in Platonic Realism?  That seems unappealing. Is it meant to represent a category so useful you would expect any rational observer to hit on it? How does it relate to the difference between the universe as it is, the universe as it is modeled, and the universe as we model it?

To what extent is this an empirical question? Are there standards for a scientific definition of life that differ from standards for a more general definition of life?

To some extent, all of the definitions discussed were pointing at the same thing. Some criteria of usefulness or rationality would be needed to differentiate between them.


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