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2 July 2015, 06:12 | Updated: 2 July 2015, 06:49
A leading Cambridge biologist claims "we are not alone'' arguing that extra-terrestrials resembling humans must have evolved on other planets.
Evolutionary biologist Simon Conway Morris says that evidence that different species will independently develop similar features means that life similar to that on Earth would also develop on other, equivalent planets.
This theory, known as convergence, suggests evolution is far from random but in fact a predictable process which follows a rigid set of rules.
It means that popular depictions of aliens with an appearance similar to humans - such as the character in the hit 1980s' film ET - may not be far from the truth.
Professor Conway Morris added that, given the growing number of Earth-like planets now discovered by astronomers, it is surprising that we have not yet discovered aliens which look and sound like us.
He added: ``I would argue that in any habitable zone that doesn't boil or freeze, intelligent life is going to emerge, because intelligence is convergent.
``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 one in 100 throws, that still leads to a very large number of intelligences scattered around, that are likely to be similar to us.''
Prof Conway Morris, a fellow at St John's College, Cambridge, puts forward the argument in his new book The Runes Of Evolution.
He argues that convergence is not just common, but everywhere, and that it has governed every aspect of life's development on Earth.
Proteins, eyes, limbs, intelligence, tool-making - even our capacity to experience orgasms - are, he argues, inevitable once life emerges.
``Often, research into convergence is accompanied by exclamations of surprise, describing it as uncanny, remarkable and astonishing,'' Prof Conway Morris said.
``In fact it is everywhere, and that is a remarkable indication that evolution is far from a random process.
``If the outcomes of evolution are at least broadly predictable, then what applies on Earth will apply across the Milky Way, and beyond.''
He has previously raised the prospect that alien life, if out there, would resemble earthlings - with limbs, heads, and bodies.
His new book goes further adding that any Earth-like planet should also evolve predators like sharks, pitcher plants, mangroves, and mushrooms, among many other things.
Limbs, brains and intelligence would, similarly, be ``almost guaranteed''.
The traits of human-like intelligence have evolved in other species - the octopus and some birds, for example, both exhibit social playfulness - and this, the book suggests, indicates that intelligence is an inevitable consequence of evolution that would characterise extra-terrestrials as well.