What Lives? A meta-analysis of diverse opinions on the definition of life

This pre-print collects together 68 definitions of life from various scientists and other thinkers and performs textual analysis on them with LLMs. I read through the individual definitions in the appendices. Here are some that caught my eye:

David Krakauer

Autonomous problem-solving matter.

Denis Noble

Life is self-creating agency.

Donald Hoffman

The distinction between living and nonliving objects is not principled. It is an artifact of the limitations of our senses. We always interact with Life, but our senses serve as interfaces that dumb things down, and thereby introduce an apparent distinction between living and nonliving.

Joshua Bongard

Information flows are discovered that are initially restricted to narrow spatial and temporal ranges, are univariate (one point source), and the carriers of information are restricted to a few energetic and physical modalities (electricity; vibration). Over time, these flows are found to multiply; expand across space and time; become multivariate and higher-order; and be carried by additional energetic and physical modalities (quantum; plasma).

Karl Friston

Life is a scale -invariant, far-from-equilibrium process with an attracting set of characteristic states (technically, pullback attractors) that (i) feature an individuation of living systems in terms of their (Markov) boundaries, (ii) which are open, in the sense there is exchange across the boundaries and (iii) breaks detailed balance, in the sense of possessing solenoidal (i.e., non-dissipative) dynamics; e.g., biorhythms, lifecycles and replication.

Michael Levin

We call alive those cognitive systems that (a) self-assemble under metabolic constraints (scarcity of time and energy, which demands essential coarse-graining and mind-full models of self and world, as well as memory reinterpretation that commits to sensemaking over fidelity), and (b) are good at scaling up the basal competencies of their parts into a new being with top-down control and a larger cognitive light cone than any of its subsystems. Living beings remember, and anticipate, coarse-graining experience into a continuous actionable dream that forms models of itself and its world, and the distinction between them. Life is a stream of temporarily persistent, coherent, agential patterns within some medium that, over time, expands its cognitive light cone and projects it into new problem spaces within which to strive.

Nick Lane

A formal definition of life is unhelpful because living is a process over time, and drawing a line across a continuum is always arbitrary. Geochemical systems that give rise to life combine continuous flow with cellular structure, as in structured hydrothermal systems that operate as electrochemical flow reactors. Environmental disequilibria convert gases such as H2, CO2 and NH3 into organic molecules through a reaction network that prefigures metabolism, from which genes emerge, meaning that growth precedes heredity.

Oded Rechavi

Anything that keeps changing in order to stay the same.

Pamela Lyon

Life is a process by which a sensitive, behaving system constructs, maintains and reproduces its own organization by taking in and using matter and energy from its surroundings selected on the basis of cognition—awareness, perception, discrimination, valuation, memory, learning—to enable agency, actions aimed at realizing internally generated goals, such as system persistence.

Paul Davies

Following Schrodinger, there is a ‘new kind of physical law’ prevailing in living matter. So we won’t have a definition until we uncover that law. What can we say about it in the interim? In my opinion, it would give causal efficacy to information, but above and beyond mere Maxwell demonics. (Life is full of Maxwell demons playing the margins of the second law of thermodynamics.) Following Landauer, ‘information is physical,’ so it is a quantity that has causal consequences. But living matter couples information networks to chemical networks, and the said ‘law’ would involve some sort of global measure of complexity. The law would be of a ‘new kind’ because it would not involve locally-defined quantities.

Philip Ball

I don’t believe we have an adequate understanding of the range of possible behaviors in complex matter to attempt any universal definition of life, but to the extent that we know them, living systems all exhibit agency: the ability to manipulate themselves and their environment to achieve autonomously determined goals. I believe that it should be possible to operationalize a notion of agency more readily than to do so for “life”. Characteristic features would include a sustained thermodynamic separation of agent and environment, and a context- and history-dependence of responses to stimuli: an agent’s behavior makes reference not just to external conditions but to internal states. In addition: evolution by natural selection is not an intrinsic property of living things, but rather, is the only mechanism currently known by which the necessary complexity for agency might arise spontaneously.

Scott Gilbert

A living entity is a bounded system of molecular processes that interact with its environment so as to use metabolism to persist. The living entity would therefore retain its identity by changing its parts

Steve Frank

In general, I believe it is almost always a bad idea to try and define something outside the context of solving a specific puzzle or working toward a specific goal. That is like deciding which tools to use before you know what you are trying to build or fix because definitions are tools and not endpoints. That is the reason that people never agree on definitions and argue endlessly and uselessly about them, there are no good definitions outside of context.

Stuart Kauffman

We have no agreed-upon definition of life. We here build toward the following: Life is a non-equilibrium, self-reproducing chemical reaction system that achieves: i) Collective autocatalysis, ii) Constraint Closure, iii) Spatial Closure, iv) As such, living entities are Kantian Wholes.

Susan Stepney

Living systems are open far-from-equilibrium self-producing systems, embodied in smart computational metamaterials, with non-trivial, irreversible meta-dynamics (where metamaterials are engineered or evolved to have special functional and/or computational behaviors, and meta-dynamics is the dynamics, or change, of the system’s own dynamics).

Theodore Pavlic

Living things are statistical novelty producers, and sometimes the products of life (viruses, computers, robots) can themselves be extensions of life that are understandably confused for the genuine article. Novelty production is really what all of the other putative necessary features of life (metabolism, growth, organization, homeostasis, reproduction, etc.) bring about. On another planet, it won’t be any particular chemical process or molecular structure that will really convince us that we have found life; it will be the repeated presence of patterns that simple historical contingency has no chance of producing continuously at scale.

Walter Fontana

Life is matter that has learned how to learn.

Wesley Wong

An operational definition of life, grounded in physical measurement, could help us recognize life in unexpected contexts. While no single definition covers all known phenomenon, approaches like Schrodinger’s definition based on statistical mechanics, and Laughlin’s framing of emergent behavior in mesoscopic systems are particularly compelling. In the end, we may not need a singular definition–instead, context-specific definitions, including those that blur the line between life and non-life, could be more useful.