The popular belief that species emerge more frequently in warmer regions is under attack, a study new suggests it's the opposite, that species evolve faster in cooler climes.
Scientists had assumed that new species develop faster in the tropics, since they are home to greater species diversity than at higher latitudes. But the researchers behind the new analysis say the explanation for this is that fewer species have gone extinct near the equator.
Jason Weir and Dolph Schluter at the University of British Columbia in Vancouver, Canada, compared how animal species across the Americas have evolved. They looked at pairs of 'sister species', which share an immediate common ancestor and so are the most closely related species.
Gene testing allowed them to estimate how long ago each pair of sister species diverged from one another. A small number of genetic differences between two species indicates that they diverged relatively recently, a larger number suggests they diverged longer ago.
Weir and Schluter compared the divergence time of various bird and mammal species in tropical regions of the Americas – stretching roughly from the middle of Mexico to the border between Bolivia and Argentina – to that of species in higher latitudes.