Evolution Diary

Christopher Lee / Washington Post

Evolution can be seen in months rather than eons, according to a new study.

A team of evolutionary biologists, led by Jonathan Losos of Harvard University, observed significant physical changes in populations of Anolis sagrei lizards less than a year after predators were introduced to the tiny islands in the Bahamas where the lizards live.

The researchers introduced the predators, also lizards, on six small islands, while leaving six other islands free of them. Anolis sagrei lizards spend most of their time on the ground, but when a new predator arrives on the scene, they retreat to trees and shrubs. Researchers figured that, at first, longer-legged lizards were the ones most likely to make it to the trees and elude predators. But natural selection also suggested that, once the species made its home in the trees, lizards with shorter limbs would be favored, since they can more easily climb through narrow branches and twigs.

Sure enough, after six months, the Anolis sagrei lizard population on the islands with the new predators had dwindled by more than half, and those that survived tended to have longer legs than lizards on islands without predators. Six months after that, the lizards on the predator islands had shorter legs than their counterparts.

The findings, published in last week’s issue of Science, illustrate that the behavioral flexibility of animals can lead to rapid shifts in evolution — and that scientists can test and observe such shifts. They also can help scientists understand the origins of biological diversity.