You can forget about little green men and predatory Xenomorphs: aliens are likely to look a lot like human beings, according to an expert in evolution from the University of Cambridge. In a new book, Simon Conway Morris says that any extra-terrestrial lifeforms will have evolved very much like we have - because an Earth-like planet would be necessary to support life in the first place.
The theory, called convergent evolution, is actually already well established: the idea is that different species evolve similar characteristics because they're living in a similar environment. One of the most commonly cited examples is the octopus camera eye, which works in much the same way as a human eye. Morris thinks that because alien species will be living on planets like our own, they'll evolve along similar lines.
It should make interplanetary diplomacy a little easier, at least.
The academic discusses the theory in a new book published this week, The Runes Of Evolution. "The book is really trying to persuade the world that evolutionary convergence is completely ubiquitous," Morris told The Independent. "Wherever you look you see it. The theme is to try and drive the reader, gently of course, into the possibility that the things which we regard as most important - cognitive sophistication, large brains, intelligence, tool-making - are also convergent."
"Therefore, in principle, other Earth-like planets should very much end up with the same sort of arrangement."
And it doesn't stop at humans either. The Cambridge professor believes that plant and animal life will probably have followed the same evolutionary pattern too. "Certainly it's not the case that every Earth-like planet will have life, let alone humanoids," he says. "But if you want a sophisticated plant it will look awfully like a flower. If you want a fly there's only a few ways you can do that. If you want to swim like a shark, there's only a few ways you can do that. If you want to invent warm-bloodedness, like birds and mammals, there's only a few ways to do that."
The book also deals with the paradox put down by Enrico Fermi: if aliens exist, why have they not yet made contact? "The problem is exceedingly acute," says Morris. "We shouldn't be alone but, famous last words, all the evidence suggests we are. Maybe [aliens] are hiding, the Arthur C Clarke idea, or as Stephen Baxter mischievously suggested, we live in a virtual world. I don't honestly know. My suspicion is we have only begun to scratch at the surface of reality, for want of a better word."
Of course there are plenty of competing ideas about what alien lifeforms look like, but if Morris is right, they could already be living among us.