STUDYING evolution is a lot like studying tigers. You know your subject is there by the traces it leaves, but you don't often see it in the flesh. This year, though, evolutionary biologists were treated to not one but several glimpses of evolution in action right before their eyes.

Take the little lizard known as Anolis sagrei. When researchers introduced a larger, predatory lizard onto the tiny Caribbean islands where they live, A. sagrei immediately began to evolve longer legs for speedier escapes. But then the little lizards learned to flee into the branches of shrubs, where the predator could not follow - and within six months evolution had changed tack again to favour shorter-legged lizards, which are better climbers.

However, such changes are small beer compared with the hard stuff of evolution: making new species. Yet here too evolution put on a show in real time. Biologists reported not one, but two butterfly species that arose abruptly from hybridisation between existing species, a form of instant speciation formerly known only in plants.