Evolution right before our eyes

19Nov06

Lizards Pushed Into Evolutionary Fast Lane

The indigenous lizard (Anolis sagrei) spends much of its time on the ground, but when a terrestrial predator is introduced, it takes to trees and shrubs, becoming increasingly arboreal over time. Losos and his colleagues hypothesized that immediately following a predator’s introduction longer-legged – and hence faster-running – Anolis lizards would be favored to elude capture. However, as the lizards grew ever more arboreal in habitat, the scientists projected that natural selection would begin to favor shorter limbs, which are better suited to navigating narrow branches and twigs.

In striking fashion, the researcher’s hypothesis was borne out. Six months after the introduction of the predator, Losos found that the Anolis population had dropped by half or more on the islands with the predators, and in comparison to the lizards on the predator-free islands, long legs were more strongly favored: Survivors had longer legs relative to non-survivors. After another six months, during which time the Anolis lizards grew increasingly arboreal, selective pressures were exactly the opposite: Survivors were now characterized by having shorter legs on the experimental islands as compared to the control islands.

This is fascinating. I’ve always thought us (humanity) lucky because evolution acts (on us, at least) so slowly that biological changes aren’t really noticeable. Can you imagine if they were? The shortchanged would be subject to intense social ostracism. Have you ever seen the movie Gattaca?

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