London: Extraterrestrials resembling humans should have evolved on other Earth-like planets, a study on convergent evolution says.
The argument emerges from leading evolutionary biologist professor Simon Conway Morris's new book 'The Runes Of Evolution'.
Conway Morris makes the case for a ubiquitous "map of life" that governs the way in which all living things develop.
He says evolution is far from random, and a predictable process that operates according to a fairly rigid set of rules.
If that is the case, then it follows that life similar to that on the Earth would also develop in the right conditions on other, equivalent planets.
Given the growing number of Earth-like planets of which astronomers are now aware, it is increasingly extraordinary that aliens that look and behave something like us have not been found, he said.
"Convergence is one of the best arguments for Darwinian adaptation, but its sheer ubiquity has not been appreciated," Conway Morris, a Fellow at St John's College, University of Cambridge, said.
"Often, research into convergence is accompanied by exclamations of surprise, describing it as uncanny, remarkable and astonishing."
"In fact it is everywhere, and that is a remarkable indication that evolution is far from a random process. And if the outcomes of evolution are at least broadly predictable, then what applies on Earth will apply across the Milky Way, and beyond," he said.
Conway Morris has previously raised the prospect that alien life, if out there, would resemble earthlings - with limbs, heads, and bodies - at a Royal Society Conference in London in 2010.
His new book goes even further, however, adding that any Earth-like planet should also evolve thunniform predators (like sharks), pitcher plants, mangroves, and mushrooms, among many other things.
Limbs, brains and intelligence would, similarly, be "almost guaranteed".
'The Runes Of Evolution' is published by Templeton Press.