Extra-terrestrials that resemble humans should have evolved on other, Earth-like planets, making it increasingly paradoxical that we still appear to be alone in the universe, the author of a new study on convergent evolution has claimed.
The argument is one of several that emerge from The Runes Of Evolution, a new book in which the leading evolutionary biologist, Professor Simon Conway Morris, makes the case for a ubiquitous "map of life" that governs the way in which all living things develop.
It builds on the established principle of convergent evolution, a widely-supported theory - although one still disputed by some biologists - that different species will independently evolve similar features.
Conway Morris 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.
The book claims that evolution is therefore far from random, but 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 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 suggests.
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