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Comment by oarla | Hacker News Reader

The article touches on this a bit, but I've always wondered what is defined as life. As noted in this article, source of complex organic compounds on Earth is most likely biological, but on other planets, the odds are pretty low for that. If life is self sustaining complex organics, then I guess the bar is pretty low to find it in the universe.

However, if life is defined as adapting complex organics(evolution), where the errors in replication of cells triggers different combinations then it gets more interesting as that is in a nutshell how life started evolving on Earth.

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It's important to note that definitions don't reflect reality so much as humans' interpretations of it.

IMHO, the life/not-life dichotomy is a false one. We observe the "lifecycle" on our own timescales, which biases our understanding of what is "living" and "not living" as distinct entities. For instance: is the planet Earth "alive"? Are geological processes synonymous with "life"?

Further, what are "organics"? If we take the biochemists' view, it's anything in which organic molecules occur. Are rocks then "alive" since they fit into this definition?

In biology 101, they taught us that life is something with the following properties:

1. Has order

2. Has metabolism

3. Has evolutionary adaptation

4. Responds to the environment

5. Reproduces

6. Grows and develops

Which seems fine as a definition, but certain physical processes are still a little ambiguous. Like consciousness, there's probably not a clear dividing line between life and non-life, but rather a gradient between the two.

Why is evolutionary adaptation a necessity? If some reasonably complex organism evolved and then perfected its DNA replication to the point where no mutations occurred, and thus it could not evolve any further, it would cease to be considered alive?

Just because no mutations are occuring doesn't mean natural selection isn't taking place, it just means that there are no fitter variants in that organism's immediate fitness landscape

Whatever definition we end up with, if it requires organic molecules from principle, it's too strict to be useful, and if does not require evolution it's way too broad for anything useful.

Is evolution real a prerequisite for life or is it just a consequence of imperfect replication of DNA? The fact that mutations can be beneficial and accumulate in a population seems more like a happy accident, rather than a fundamental part of life. But then again, I'm no biologist.

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