Evolution Occurs When Species Stay in Place, Not by Landscape Changes

There may be a new theory when it comes to the process of evolution. Scientists have discovered that dramatic changes in a landscape may not drive species divergence. Instead, it could be that a species' ability to move may play a far greater role.

Birds that are related, such as Darwin's finches, but that vary in beak size and behavior specifically evolved to their habitat are examples of a process called speciation. Essentially, one species becomes many as the birds evolve and adapt to their environment. For years, researchers believed that speciation occurred due to dramatic geographical changes, such as the formation of the Andes Mountain range or the Amazon River. Now, though, scientists have come up with a different solution.

"The extraordinary diversity of birds in South America is usually attributed to big changes in the landscape over geological time, but our study suggests that prolonged periods of landscape stability are more important," said Robb Brumfield, one of the lead authors of the new study, in a news release. "By using detailed sampling of many bird lineages, we were able to get a clearer and larger picture of when and how species formed within those lineages."

More specifically, the researchers examined the genealogy of 27 species of birds in the Neotropics, a region which extends from southern Mexico through Central America to southern Brazil and includes the Amazon rainforest. By looking at this genetic data, the scientists found multiple accounts of species divergence that varied over time. This, in particular, showed that the Andes Mountains were not the primary cause of speciation. Instead, it had an indirect effect on diversification as a semi-permeable barrier.

What was more interesting was the fact that the longer length of time a species inhabited an area, the more likely it was to disperse and diverge. It addition, the less mobility a species had, the more likely it would diverge.

"Our results suggest that human alterations of the landscape can effectively kill the speciation process," said Brumfield.

The findings are published in the journal Nature.