How Evolution Brought a Flightless Bird Back From Extinction

Fossil remains offer rare evidence of a phenomenon known as ‘iterative evolution’

Brigit Katz
Correspondent
May 13, 2019

Around 136,000 years ago, the Aldabra atoll in the Indian Ocean was inundated by a major flood that wiped out all the terrestrial animals that lived there—among them a species of flightless bird called the Aldabra rail. Tens of thousands of years later, sea levels fell back, once again making life possible on the atoll. And, according to a new study, the once-extinct Aldabra rail came back.

Writing in the Zoological Journal of the Linnean Society, Julian Hume of the Natural History Museum at Tring in the U.K. and David Martill of the University of Portsmouth explain that this feat of resurrection was made possible by “iterative evolution”—a rare process that involves the evolution of “similar or parallel structures” from the same ancestral lineage, but at different times. Or, as Sophie Lewis of CBS News, puts it, iterative evolution means that “species can re-emerge over and over, despite past iterations going extinct.”

The Aldabra rail is a subspecies of the white-throated rail (Dryolimnas cuvieri), which is indigenous to islands in the southwestern Indian Ocean. The birds are “persistent colonizers,” according to the University of Portsmouth; they are known to build up on large land bodies and subsequently depart en masse, possibly triggered by overcrowding and a lack of food.

“Something sets them off and they fly in all directions,” Hume tells Josh Davis of the Natural History Museum. “It can happen every fifty years or every hundred years. People still don't really understand it, but if the birds are lucky some of them will land on an island.”

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