Lizards Pushed Into Evolutionary Fast Lane:
"Evolutionary change is generally considered to be a pedestrian affair, with changes occurring over millennia. But evolutionary biologists from Harvard have shown that natural selection can occur within months, as a population's needs change. Their study, appearing in the journal Science, was based on populations of the lizard Anolis sagrei that inhabits cays (small islands) in the Bahamas, and what happened when a new predator was introduced. The scientists found that natural selection dramatically reversed direction over a very short period, first favoring longer, and then shorter, hind legs.
Experiments where researchers are able to witness evolution in action have been something of a rarity. 'Recent work has shown, however, that evolutionary biology can be studied on short time scales and that predictions about it can be tested experimentally. We predicted, and then demonstrated, a reversal in the direction of natural selection acting on limb length in a population of lizards,' explained Harvard's Jonathan B. Losos."