Posted by: dacalu | 20 March 2012

What is Life?

I promise to return to the subject of the holistic perspective soon.  Too many interesting things to think about, though.

For the last 7 months or so, I have been thinking about questions of how we define life.  Last night it struck me that the question is intimately wrapped up in why we’re asking it.  Scientists and philosophers have gotten quite tangled up in this question, from Aristotle to astrobiology.  So many things look like life – fire, crystals, robots – without actually being life.  [Curiously, the last is evidence of life, even though it, itself, is not alive.]  Two of the most popular definitions are the Pornography Definition (I couldn’t say exactly, but I know it when I see it), and the Syndrome Definition (If you have 5 of these 15 symptoms, chances are good you have life.  It can’t be cured, but we can mitigate the effects).  Philosophers find both of these immensely unsatisfying, because they are so biased toward what we already know, so fuzzy about making predictions.  More satisfying, but alas not fully accurate definitions have included:

The ability to replicate (but crystals and fire)

The ability to replicate imperfectly (but still, crystals and fire)

The ability to replicate well, but imperfectly with imperfections transmitted to offspring. (This is roughly Darwinian evolution and shows some promise.  Alas, it begs the question “over what timescale.”  It also means sterile individuals are not alive…)

Metabolism (but hot, muddy water and comets on very long time scales)

The ability to digest nutrients and make energy (but fire)

The ability to digest nutrients and turn them into fuel (but stars)

Local an-entropy (but what scale constitutes local?)


The list goes on.  It’s sort of a fun exercise, but can get frustrating after a while.  Pondering this question over a few very dense articles, it occurred to me that not everyone is asking for the same reason.  There seem to be some fundamental human reasons for wanting to identify life.

1) Can I eat it?

2) Will it eat me?

3) Can I mate with it?

Once you add a little abstract thought, you get

4) Will it compete with me for some resource?

5) Can we cooperate and or communicate?

And one more step removed

6) Can I learn something from it.


A surprising amount of the conversation revolves around number 6.  I admit, that’s where my thoughts go.  It’s really exciting to think about discovering new forms of life so that we can compare them to known forms of life.  It’s interesting to think about test cases and borderlines.  It makes academics happy.

Alas, 6 turns out to be the most abstract, least visceral question.  No wonder astrobiologists get some of our best press from the Search for Extra-Terrestrial Intelligence (SETI); that at least drops us down to number 5.  Still, I wonder how much of the public is more interested in 1 and 2.  I also wonder why so many of us in the academic “definition of life” community have spent so little time really looking at numbers 1-4 as serious questions.  Something to think about.



  1. Lucas everything you write is a hoot. I love it. You must be having the time of your life. hiram

    • I am. Thanks.

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