(This post is part of the attempt to do a write up after every Cambridge_UK meetup, of something raised at the meetup.)
What is life?
Eliezer, in "The First World Takeover", talks about the search for objects with increasing numbers of bits of functional complexity. He framed the difference between life, and the previous non-living universe, as being the introduction of self-replicators who could search for self-replicators with an improved ability to search.
In terms of organisms that share genes among a population via sexual reproduction, we have to consider this search mechanism (evolution by natural selection) to be a property of a population rather than of a single individual.
And, indeed, when we take into account the speed limit and complexity bound for evolution, what we're looking for is a population who search faster than the natural decay rate imposed by copying fidelity, genome size and how many harmful mutations get dropped each generation by the fraction of the population that don't reproduce.
And that is relative to the environment the population happens to find themselves situated in. Radiation affects mutation rate. Harshness of the environment (including competitors) determines whether the population is viable (replacement rate at least equals the death rate) or whether they will spiral down into extinction.
So maybe, rather than asking whether an individual or system of individuals counts as a life form, perhaps a more well defined question would be to ask whether they count as a viable searcher relative to a specific environment.
Why does that distinction matter?
Are prions living? How about viruses? Crystals?
We know that a turing complete machine can be implemented in Conway's Game of Life and that, given a very specific environment, crystals can not only self-replicate, but also pass on information to their 'off-spring'. So it would make sense to say that a system of crystals might be constructed that would be 'alive' relative to a specific environment that permitted the system to evolve - to 'search' not just for a variant replicator that might be improved in some limited way (such as replicating faster), but search unlimited bits of search space, including for an improved searcher.
Whereas a virus or prion would not count, unless in a particular environment the information they pass from generation to generation is able to alter the 'search' mechanism (the machinery that replicates them) in a way that can improve how it 'searches'.
The topic was raised at the meet-up, by the way, over the question of under what circumstances it would make sense to count as being alive, self-replicators made of synthetic RNA. A definitive answer wasn't reached. Any opinions?
(Please note, I'm not an expert in these areas, just writing up the report, so any mistakes are mine, not those of the meet-up participants who generated the specific ideas.)