Dr Conway-Morris has arrived at this view from a detailed study of what is known as convergent evolution.

ECONOMIST: Evolution

For example, in a few minutes, and without even leaving Wikipedia, you can travel from the Tasmanian Devil to Tasmanian devils to Tasmanian tigers to thylacines to convergent evolution.

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That similarity, though, is almost certainly the result of convergent evolution rather than a common origin, since the last joint ancestor of Crassicorophium and spiders lived way longer ago than the ancestor of Crassicorophium and barnacles.

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