A new study has found that species living together are not forced to evolve differently to avoid competing with each other, challenging a theory that has held since Darwin's Origin of Species.
By focusing on ovenbirds, one of the most diverse bird families in the world, the Oxford University-led team conducted the most in-depth analysis yet of the processes causing species differences to evolve.
They found that although bird species occurring together were consistently more different than species living apart, this was simply an artefact of species being old by the time they meet. In fact, once variation in the age of species was accounted for, coexisting species were actually more similar than species evolving separately, opposite to Darwin's view which remains widely-held today.
'It's not so much a case of Darwin being wrong, as there is no shortage of evidence for competition driving divergent evolution in some very young lineages,' said Dr Joe Tobias of Oxford University's Department of Zoology, who led the study. 'But we found no evidence that this process explains differences across a much larger sample of species.
'The reason seems to be linked to the way new species originate in animals, which almost always requires a period of geographic separation. By using genetic techniques to establish the age of lineages, we found that most ovenbird species only meet their closest relatives several million years after they separated from a common ancestor. This gives them plenty of time to develop differences by evolving separately.'
The study, published in Nature, compared the beaks, legs and songs of over 90% of ovenbird species. To tackle the huge challenge of sequencing genes and taking measurements, Oxford University scientists were joined by colleagues at Lund University (Sweden), Louisiana State University, Tulane University (New Orleans) and the American Museum of Natural History (New York).
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