Meeting 4.5 – Life and Death

The group met on 7 April to talk about concepts of life and death, both in biology and in the general public.

The meaning of “life” and “death” appear to be intuitively obvious until we start asking specifically “what is it that is alive?” “Organism” can be a tricky concept. The term implies that something is organized, but science would reject the questions “by whom?” and “for what end?” We might accept “by what?” (natural selection) and “to what end?” (reproductive success), but when we attempt precision – and prediction – using these answers, we find them elusive.

It can be useful to distinguish between the person, the organism, and the system, all of which might be considered alive, but not in the same way.


Peterson, Michael, William Hasker, Bruce Reichenbach, and David Basinger (2010) Philosophy of religion: selected readings. Oxford University Press. pp. 461-464.

Does some aspect of the person persist through death? Christians have claimed that people persist through death or are, in some way, reconstituted after death? Note that these are very different positions.

Humans may have an immortal component that survives, usually called a soul. (Plato, Augustine, Ibn Sina, Maimonides, Ibn Rushd, Aquinas; not Biblical)

Alternatively, God may recreate individuals in the world to come. (Also Aquinas)

It is important to ask what persists in either case. Will the memory be retained? The character? The relationships? The will? Different authors construct this differently. General consensus holds that “self” will persist, but what is self?

Dualist interpretations often make the physical organism corruptible and the spiritual or mental intellect immortal. (Plato, Descartes)

Is there a difference between a continuous person (Locke claimed that identity is continual consciousness, though sleep may be a problem here) and a recreated person (John Hick imagines God creating a replica of the individual from memory)?

How would we convince ourselves of life after death? Authority? A priori arguments (e.g., Plato, Kant)? A posteriori arguments (e.g., resurrection or transmission of information from a non-physical entity to a physical observer)? Note that the question of resuscitation vs. resurrection is one of continuity vs. recreation. Is this tractable in science?

Hindu, Buddhist, and Taoist thinkers suggest that the question is poorly framed. Aspects of life may be passed on (e.g., karma) without any individual or essential self. If there is transmission, what is the unit of transmission? Alternatively, there may be only one self (e.g., Atman) existing in multiple manifestations. The discussion hangs on ontology – what fundamental things you can talk about.

MIX 2015

Mix, LJ. (2015) Defending definitions of life. Astrobiology. 15(1): 15-19.

What do we mean when we use these words in science: life, alive, living, biological (of life), metabolic (of living chemistry)… ?

Pornography Definition: “I can’t say what it is, but I know it when I see it.” This is too vague to do work but still popular. What ontology does it cover?

Woese Life: possessing small subunit rRNA. When talking about life, we frequently specifically about Earth life, which shares a number of common features, including information processing via ribosomes. We could be explicit about when we are talking about this set of things, or any set constructed via phylogenetic tree.

Darwin Life: exhibiting evolution by natural selection. This is one of the most popular definitions of life in the current literature. I suggest that it is really a research program rather than a definition because evolution is poorly characterized with regards to individuals. What are the units of selection? What are the units of inheritance? Are they the same, and if not, which of the two is alive? We are accustomed to speaking of generations as the time between fertilizations in sexually reproducing species, but this does not cover the vast majority of life on Earth. Do gametophytes count as alive? Gametes? Seeds? Spores? Viruses? Plasmids? Transposons? What about things that replicate in silico?

Haldane Life: exhibiting metabolism and maintenance. This is the other most popular definition, but faces similar problems. What unit will we use? This becomes particularly clear when we speak of organisms? Where do we draw the lines? Humans are obligate symbionts with our microflora; does that make us one organism? At what point do endosymbiotic parasites become organelles? Are our prostheses part of us? Does a nuclear reactor count as metabolic? It cannot persist without human maintenance and supports human survival.

Note that Haldane life captures the difference of alive vs. dead as well as living vs. non-living. The other definitions do not and must include fossils and artifacts (iPhones have selected, variable, heritable code components).

When an individual organism of Homo sapiens dies but genes, cells, even tissues may persist. To what, if any, physical phenomenon do we attach personhood? What would the consequences be for euthanasia, medicine, reproductive technologies, and inheritance?

As a biological concept, when we speak of genes persisting through generations, we are really talking about gene “types” persisting, rather than specific polynucleotide. This is usually and ideal concept of type and not empirical. What do we mean? Is it the information content that we maintain? Information in this sense is not separable from an interpreter. Who (what) is the interpreter? How much variation do we allow before it is a new type? Such questions will be necessary to mathematize our Darwinian concept of life and, I think, necessary to consider it properly empirical.

For more on this topic, check out last semester’s discussions, starting here


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