Evolution Of Species Does Not Always Follow Darwin's Theories
December 23, 2013

Creatures Living Together Don’t Have To Evolve Differently After All

redOrbit Staff & Wire Reports - Your Universe Online

Evolutionary scientists have long argued that species that live together must evolve in different ways in order to avoid direct competition with each other, but new research published Sunday in the journal Nature suggests otherwise.

A team of researchers led by Dr. Joe Tobias of Oxford University's Department of Zoology studied ovenbirds, one of the most diverse families of birds in the world, in order to conduct an in-depth analysis of the processes that result in the evolution of species differences.

They found that even though bird species that occurred together were typically more varied than those that lived apart, this was “simply an artifact of species being old by the time they meet,” the researchers said. Once differences in the age of species was accounted for, they found that coexisting species tended to be more similar than those types of birds that evolved separately – the opposite of what Charles Darwin claimed in Origin of Species.

“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,” Dr. Tobias said in a statement. “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,” he added. “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.”

As part of their research, Dr. Tobias and colleagues from Lund University in Sweden, Louisiana State University, Tulane University and the American Museum of Natural History compared the beaks, legs and songs of more than 90 percent of all ovenbird species, taking measurements and sequencing genomes.

While the legs and beaks of species living together tended to be no more different than those living apart, the researchers found that their songs were actually more similar. This discovery was a surprise, as it had long been assumed that bird species living close to each other would need to develop different songs to avoid confusion.

“Looking at the bigger picture, 'be different or die' doesn't appear to explain evolution,” Dr. Tobias explained. “Ovenbird species use a wide variety of beaks, from long and hooked to short and straight, but these differences appear to evolve when living in isolation, suggesting that competition is not the major driving force producing species differences. Instead, it seems to have the opposite effect in promoting the evolution of similar songs.”

“The reasons for this are difficult to explain and require further study, but they may have something to do with the advantages of using the same 'language' in terms of similar aggressive or territorial signals,” he added. “For instance, individuals of two closely related species with similar songs may benefit because they are able to defend territories and avoid harmful territorial contests not only against rivals of their own species but those in other species coexisting in the same places and competing for similar resources.”

Image 2 (below): A phylogenetic tree illustrating evolutionary relationships and beak variation among 350 lineages of ovenbirds. Credit: Joseph A. Tobias and D. Seddon, images reproduced with the permission of Lynx Edicions