From Science:
With crushing heat and humidity, you’d think life would move sluggishly in tropical rainforests. But according to a new study, at least one thing proceeds more like the hare than the tortoise: molecular evolution. Faster evolution in the tropics than more temperate zones could help explain why rainforests are such hotbeds of diversity and have implications for how scientists calculate when one species diverged from another.
Scientists have uncovered hints that evolution progresses faster in regions closer to the equator than in those closer to the poles. But this consensus was never backed up with a solid explanation. “Nobody’s tested it properly,” says evolutionary ecologist Len Gillman of the Auckland University of Technology in New Zealand. One theory is that the tropics’ smaller population sizes make it easier for random genetic changes to accumulate and increase the genetic differences between populations. Another is that the faster metabolism of tropical species, spurred by hotter temperatures and more sunlight, offers more opportunities for cell division to go awry. This could lead to potentially useful DNA mutations.
More here.