Could it be that our species is the principal indigenous race in the Universe – that Homo sapiens, or something close to it, has evolved independently on multiple other worlds?
The late evolutionary biologist Stephen J Gould found this idea preposterous. He argued that if you re-ran evolution here on Earth – never mind on some bonkers planet 300 light-years away – then the probability of getting humans a second time round is vanishingly small.
But it’s a view that’s not universally held. One school of thought, called ‘convergent evolution’, says that random effects eventually average out so that evolution converges, tending to produce similar organisms in any given environment. For example, flight has evolved independently on Earth at least four times – in birds, bats, insects and pterosaurs.
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“One can say with reasonable confidence that the likelihood of something analogous to a human evolving is really pretty high. And given the number of potential planets that we now have good reason to think exist, even if the dice only come up the right way every 1 in 100 throws, that still leads to a very large number of intelligences scattered around, that are likely to be similar to us,” [said professor Simon Conway Morris].
