The November 26th issue of the journal Science included a study showing that the extinction of the dinosaurs some 65 million years ago allowed puny mammals to get really big. But well before all that happened, another event triggered a different burst of evolutionary activity.

A new study finds that about 300 million years ago, the tropical rainforests along the equator fell apart. The familiar culprit—global warming.

Present-day Europe and North America were on the equator back then, and were covered with rainforests. But global warming made things even hotter and drier.

The expansive rainforests broke up into smaller fragments, and reptile populations became isolated from each other in the fragments. Such geographical isolation allows different populations to evolve in different directions, which led to a great increase in reptile diversity. The research appears in the journal Geology. [Sarda Sahney, Michael Benton, and Howard Falcon-Lang, "Rainforest collapse triggered Carboniferous tetrapod diversification in Euramerica"]

The explosion in reptiles ultimately led to the evolution of the dinosaurs, which dominated the planet until they fell victim to the massive impact that allowed us mammals to take over. As Vonnegut would say, so it goes.

—Steve Mirsky

[The above text is an exact transcript of this podcast.]