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EVOLUTION is a fact of life, at least of life as we know it. Here on Earth, organisms that just so happen to be better adapted, or 鈥渇it鈥�, for their environment, perhaps by virtue of a fortuitous mutation, tend to survive longer and leave more offspring. The less fit leave fewer descendants and the unfit none at all. Whatever it was that made the winners fit thus accumulates in the next generation, a cruel and random Squid Game called evolution by natural selection.

As to why it happens, on one level that鈥檚 simple. According to biologist Richard Dawkins, evolution is simply a change in gene frequencies in populations. If a gene in a colony of woodlice living under a dead log becomes more or less common for some reason, evolution has happened.

But must it be like that? All life on Earth that we know of comes from the same origin and uses the same biochemical operating system based on DNA. Putative life on other planets, or 鈥渟hadow life鈥� from an independent origin on Earth, might conceivably operate under very different rules. Does life have to evolve 鈥� and if so, does that have to be by natural selection? 鈥淭hat鈥檚 a very interesting and large question,鈥� says Dawkins.

, author of , thinks the alternatives are limited. One might be to postulate an intelligent designer, as perhaps we ourselves might someday design self-replicating organisms. But that only gets you so far, says Kershenbaum. 鈥淚t鈥檚 definitely a possibility we could find planets covered in artificial life,鈥� he says. 鈥淏ut then you have to explain where the designers, the original life, came from.鈥�

And in that recursion, you hit the nub of the matter. 鈥淓ssentially, the mechanism by which life arises is accumulation of complexity, and that complexity doesn鈥檛 come from nowhere and it can鈥檛 arise by chance,鈥� says Kershenbaum. Purely thermodynamically, it must arise step by step.

The spontaneous, sustained accumulation of complexity in a system requires three things to be present. There must be variation, to give raw material for change in the first place; there must be differences in fitness, to give an advantage to change; and there must be heritability, to consolidate and pass on change over time. These three things are nothing more than the preconditions for natural selection 鈥� and wherever they come together, natural selection inevitably follows.

The operating system itself matters not a jot. 鈥淭he biology is irrelevant,鈥� says Kershenbaum. 鈥淚t doesn鈥檛 matter what the biochemistry is, it doesn鈥檛 matter if it鈥檚 silicon-based or methane-based.鈥� Even if a different type of life got going, it is hard to see how it could persist without mutation and selection to make it fitter and provide resilience to slate-wiping events in a world that is itself dynamic and changing. Kershenbaum proposes that evolution is a law of nature, a bit like gravity. Where there is life to ask the question, there is evolution.

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