Evolution's "Driving Force" Shifts Based on Behavior, Study Says

Brown anole lizards on tiny islands in the Bahamas were enjoying the good life, untroubled by a lizard predator found on larger islands nearby.

But all that changed when biologist Jonathan Losos of Harvard University in Cambridge, Massachusetts, appeared on the scene.

Losos's team experimentally introduced predatory curly-tail lizards onto six islands where the ground-dwelling anoles had been living free of predators, sparking a see-saw year of natural selection.

For the smaller anole lizards, a trait that was advantageous in November—six months after the introduction—had become a liability by May.

Initially the longer-legged anoles were more likely to avoid being eaten, due to their faster running speed.

But as the anoles increasingly sought safety in trees, where the bulky curly-tails could not pursue them, shorter-legged lizards were favored for their superior climbing ability.