Welcome to brain Stuff production of iHeart Radio. Hey brain Stuff, Lorn Vogel Bomb. Here out in the Indian Ocean, about two hundred and fifty miles or four hundred kilometers to the northwest of Madagascar, there's a shallow lagoon encircled by a ring of islands. Those outcrops make up the Aldabra Atoll, a place where mangroves flourish and one hundred thousand giant tortoises roam free. Recently, a different resident caught the world's attention.
The Aldabra rail is a chicken sized bird found exclusively on the atoll. It's also the only remaining island bird in the Indian Ocean that happens to be flightless. Weak arm muscles and asymmetrical flight feathers keep the bird grounded, yet its ancestors could fly. The Aldabra rail evolved from the white throated rail, a still living bird that flies very well. Thank you. White throated rails inhabit Madagascar and neighboring islands. Thousands of years ago, a number of these
birds flew out to the Aldabra Atoll. Then, as now, large predators were rare on the atoll, but the thread of predation mostly gone, the bird's descendants gradually lost the ability to fly. That same thing happened to the dodo, another island dwelling bird whose ancestors surrendered flight. Flying is a high energy activity. When there's no need to fly away from predators and you can get food simply by walking around, why waste the energy on the Aldabra toll.
Flight became unnecessary for short term survival, So over many generations, the isolated rail population gave rise to the fully flightless birds we know today. But it turns out there's a startling plot twist. Apparently the sequence of events we just described happened more than once. A twenty nineteen studies suggests that flighted colonizing rails came to Aldabra and begot a non flying subspecies on two different occasions. It's as if
natural selection hit the reset button. Scientists call the phenomenon iterative evolution. Today, we're going to explain what this process entails and what it doesn't. University of Partsmith biologists Julian P. Hume and David Martil co authored the groundbreaking new study, which appeared in the Zoological Journal of the Linean Society. Since their paper was published, Hume and Martell's work has garnered a lot of press coverage. Unfortunately, their findings have
been widely misinterpreted. To hear, some media outlets tell it the modern Aldabra rail went extinct and then resurrected itself from the dead. But that's not what happened, and it's not how iterative evolution works. Photographers love the Aldabra Toll for its sunny beaches and blue lagoon. If you're a paleontologist, the islands have another draw a bountiful fossil record going back hundreds of thousands of years. On elate piccard the westernmost island, a dig site has yielded a pair of
fossilized arm bones from prehistoric rails. Geologic clues tell us the bones are more than a hundred and thirty six thousand years old. It looks like the dead birds could have used a good flood insurance policy. Judging by the distribution of marine fossils like oceanic mollusk remains, it appears the atoll was totally submerged under water multiple times in
the past four hundred thousand years. More we sently the islands disappeared beneath the waves were about a hundred and thirty six thousand to a hundred and eighteen thousand years ago due to a rise in sea levels. Afterward, the waters were treated and the atoll re emerged. And now here's where the story takes an unexpected turn. The elip card arm bones look almost identical to the ones we see in living Aldabra rails today, which, as you'll recall,
are flightless. Therefore, the birds those fossils belonged to probably couldn't fly either. So theoretically, when the atoll flooded, the prehistoric rails in question were unable to escape and got wiped out. However, the saga didn't end there. As human Martel explain in their paper, the fossilized footbone of a much more recent rail was once extracted from Grand Terror,
another island in the atoll. That specimen is only about a hundred thousand years of age ergo its owner lived after the sea levels went back down and the algebra atoll resurfaced. In an intriguing case of deja vous, this fossil closely resembles the bow in today's non flying Aldabra rail and the assumption rail a bird that went extinct in ninety seven. A primary sources indicate that it was flightless too, but chances are the grand Terra fossil came from a bird that either couldn't fly or was in
the process of losing its ability to do so. Either way, it was the probable ancestor of modern aldebra rails. According to human Martil, we're looking at an evolutionary do over. The flightless birds that died out when the atoll went under had descended from an ancestral stock of high soaring rails. Once the islands vanished and then re emerged, those aerial wanderers repopulated the atoll and evolved into an all new
flightless subspecies, one that's still at large today. History repeated itself loud and clear, and that's iterative evolution and a nutshell. Iterative evolution can be defined as the repeated evolution of a specific trait or body plan from the same ancestral lineage at different points in time. Let's say there's an organism or a closely related group of organisms with a fairly conservative build that manages to survive over a long
period of geologic time. If multiple groups of similar looking descendants independently evolved one after another from this common ancestor. It would be a clear cut case of iterative evolution. Consider the ammonites, spiral shelled relatives of squids and nautilus is. Ammonites roamed the oceans throughout the age of dinosaurs. Some experts think that individuals with thinner shells that were compressed from side to side were better suited for shallow environments
with very fast currents. On the other hand, thicker, heavier shells nicely lent themselves too deep areas far off shore, So there's evidence that in certain parts of the world, an ancestral stock of thick shelled ammonites would periodically give rise to thin shelled descendants who invaded beachside habitats. When the sea levels fell, many of those habitats disappeared and
the offshoot ammonites died out. But their thick shelled ancestors persisted, and when the oceans rose again, they'd sire a new generation of shallow water denizens with thin shells. And that's just one example. Innerative evolution might also explain the repeated rise and fall of similar looking sea cows over the past twenty six million years. Likewise, sea turtles, specifically the ones with seagrass centered diets, may have undergone the same
process during their evolutionary history. While natural selection is a powerful force, cannot revive an extinct species, but when the environmental conditions are right, you can at least produce a good imitation. Today's episode was written by Mark Vancini and produced by Tyler Clang. Brain Stuff is a production of iHeart Radio's How Stuff Works. For more in this lots of other topics topics topics, visit our home planet, how
stuff Works dot com. And for more podcasts for my heart Radio, visit the iHeart Radio app, Apple Podcasts, or wherever you listen to your favorite shows.