WEBVTT - Can the Same Animal Evolve Twice? 0:00:01.920 --> 0:00:07.120 Welcome to brain Stuff production of iHeart Radio. Hey brain Stuff, 0:00:07.200 --> 0:00:10.559 Lorn Vogel Bomb. Here out in the Indian Ocean, about 0:00:10.560 --> 0:00:13.039 two hundred and fifty miles or four hundred kilometers to 0:00:13.039 --> 0:00:16.400 the northwest of Madagascar, there's a shallow lagoon encircled by 0:00:16.400 --> 0:00:19.959 a ring of islands. Those outcrops make up the Aldabra Atoll, 0:00:20.200 --> 0:00:22.960 a place where mangroves flourish and one hundred thousand giant 0:00:23.000 --> 0:00:27.520 tortoises roam free. Recently, a different resident caught the world's attention. 0:00:27.920 --> 0:00:30.920 The Aldabra rail is a chicken sized bird found exclusively 0:00:30.960 --> 0:00:34.160 on the atoll. It's also the only remaining island bird 0:00:34.200 --> 0:00:37.240 in the Indian Ocean that happens to be flightless. Weak 0:00:37.360 --> 0:00:40.440 arm muscles and asymmetrical flight feathers keep the bird grounded, 0:00:41.320 --> 0:00:45.080 yet its ancestors could fly. The Aldabra rail evolved from 0:00:45.120 --> 0:00:47.520 the white throated rail, a still living bird that flies 0:00:47.640 --> 0:00:51.199 very well. Thank you. White throated rails inhabit Madagascar and 0:00:51.240 --> 0:00:54.160 neighboring islands. Thousands of years ago, a number of these 0:00:54.200 --> 0:00:57.760 birds flew out to the Aldabra Atoll. Then, as now, 0:00:58.120 --> 0:01:01.000 large predators were rare on the atoll, but the thread 0:01:01.000 --> 0:01:04.120 of predation mostly gone, the bird's descendants gradually lost the 0:01:04.160 --> 0:01:06.959 ability to fly. That same thing happened to the dodo, 0:01:07.080 --> 0:01:11.400 another island dwelling bird whose ancestors surrendered flight. Flying is 0:01:11.400 --> 0:01:13.959 a high energy activity. When there's no need to fly 0:01:14.000 --> 0:01:16.400 away from predators and you can get food simply by 0:01:16.400 --> 0:01:20.199 walking around, why waste the energy on the Aldabra toll. 0:01:20.440 --> 0:01:24.920 Flight became unnecessary for short term survival, So over many generations, 0:01:25.040 --> 0:01:28.000 the isolated rail population gave rise to the fully flightless 0:01:28.040 --> 0:01:30.600 birds we know today. But it turns out there's a 0:01:30.600 --> 0:01:34.000 startling plot twist. Apparently the sequence of events we just 0:01:34.040 --> 0:01:38.000 described happened more than once. A twenty nineteen studies suggests 0:01:38.040 --> 0:01:41.240 that flighted colonizing rails came to Aldabra and begot a 0:01:41.280 --> 0:01:45.000 non flying subspecies on two different occasions. It's as if 0:01:45.080 --> 0:01:49.040 natural selection hit the reset button. Scientists call the phenomenon 0:01:49.160 --> 0:01:52.920 iterative evolution. Today, we're going to explain what this process 0:01:53.040 --> 0:01:58.440 entails and what it doesn't. University of Partsmith biologists Julian P. 0:01:58.680 --> 0:02:01.960 Hume and David Martil co authored the groundbreaking new study, 0:02:02.160 --> 0:02:05.200 which appeared in the Zoological Journal of the Linean Society. 0:02:05.520 --> 0:02:08.040 Since their paper was published, Hume and Martell's work has 0:02:08.080 --> 0:02:11.360 garnered a lot of press coverage. Unfortunately, their findings have 0:02:11.480 --> 0:02:15.000 been widely misinterpreted. To hear, some media outlets tell it 0:02:15.280 --> 0:02:18.320 the modern Aldabra rail went extinct and then resurrected itself 0:02:18.320 --> 0:02:20.680 from the dead. But that's not what happened, and it's 0:02:20.760 --> 0:02:25.079 not how iterative evolution works. Photographers love the Aldabra Toll 0:02:25.160 --> 0:02:28.600 for its sunny beaches and blue lagoon. If you're a paleontologist, 0:02:28.720 --> 0:02:31.840 the islands have another draw a bountiful fossil record going 0:02:31.880 --> 0:02:35.680 back hundreds of thousands of years. On elate piccard the 0:02:35.680 --> 0:02:38.160 westernmost island, a dig site has yielded a pair of 0:02:38.200 --> 0:02:42.440 fossilized arm bones from prehistoric rails. Geologic clues tell us 0:02:42.480 --> 0:02:44.200 the bones are more than a hundred and thirty six 0:02:44.200 --> 0:02:47.399 thousand years old. It looks like the dead birds could 0:02:47.400 --> 0:02:50.560 have used a good flood insurance policy. Judging by the 0:02:50.600 --> 0:02:54.480 distribution of marine fossils like oceanic mollusk remains, it appears 0:02:54.480 --> 0:02:57.400 the atoll was totally submerged under water multiple times in 0:02:57.400 --> 0:03:00.560 the past four hundred thousand years. More we sently the 0:03:00.600 --> 0:03:03.079 islands disappeared beneath the waves were about a hundred and 0:03:03.120 --> 0:03:05.880 thirty six thousand to a hundred and eighteen thousand years 0:03:05.919 --> 0:03:09.600 ago due to a rise in sea levels. Afterward, the 0:03:09.639 --> 0:03:13.040 waters were treated and the atoll re emerged. And now 0:03:13.200 --> 0:03:16.560 here's where the story takes an unexpected turn. The elip 0:03:16.680 --> 0:03:19.280 card arm bones look almost identical to the ones we 0:03:19.320 --> 0:03:23.000 see in living Aldabra rails today, which, as you'll recall, 0:03:23.040 --> 0:03:27.160 are flightless. Therefore, the birds those fossils belonged to probably 0:03:27.160 --> 0:03:31.400 couldn't fly either. So theoretically, when the atoll flooded, the 0:03:31.480 --> 0:03:34.520 prehistoric rails in question were unable to escape and got 0:03:34.600 --> 0:03:38.640 wiped out. However, the saga didn't end there. As human 0:03:38.720 --> 0:03:41.840 Martel explain in their paper, the fossilized footbone of a 0:03:41.920 --> 0:03:44.800 much more recent rail was once extracted from Grand Terror, 0:03:45.120 --> 0:03:48.360 another island in the atoll. That specimen is only about 0:03:48.360 --> 0:03:51.560 a hundred thousand years of age ergo its owner lived 0:03:51.600 --> 0:03:54.120 after the sea levels went back down and the algebra 0:03:54.200 --> 0:03:58.320 atoll resurfaced. In an intriguing case of deja vous, this 0:03:58.400 --> 0:04:01.760 fossil closely resembles the bow in today's non flying Aldabra 0:04:01.920 --> 0:04:04.600 rail and the assumption rail a bird that went extinct 0:04:04.600 --> 0:04:07.440 in ninety seven. A primary sources indicate that it was 0:04:07.440 --> 0:04:11.200 flightless too, but chances are the grand Terra fossil came 0:04:11.240 --> 0:04:13.240 from a bird that either couldn't fly or was in 0:04:13.280 --> 0:04:16.479 the process of losing its ability to do so. Either way, 0:04:16.520 --> 0:04:20.640 it was the probable ancestor of modern aldebra rails. According 0:04:20.680 --> 0:04:23.520 to human Martil, we're looking at an evolutionary do over. 0:04:24.000 --> 0:04:26.160 The flightless birds that died out when the atoll went 0:04:26.240 --> 0:04:29.560 under had descended from an ancestral stock of high soaring rails. 0:04:30.080 --> 0:04:32.760 Once the islands vanished and then re emerged, those aerial 0:04:32.800 --> 0:04:36.120 wanderers repopulated the atoll and evolved into an all new 0:04:36.240 --> 0:04:41.200 flightless subspecies, one that's still at large today. History repeated 0:04:41.200 --> 0:04:45.040 itself loud and clear, and that's iterative evolution and a nutshell. 0:04:46.200 --> 0:04:49.279 Iterative evolution can be defined as the repeated evolution of 0:04:49.320 --> 0:04:52.160 a specific trait or body plan from the same ancestral 0:04:52.160 --> 0:04:55.520 lineage at different points in time. Let's say there's an 0:04:55.560 --> 0:04:58.359 organism or a closely related group of organisms with a 0:04:58.400 --> 0:05:01.520 fairly conservative build that manages to survive over a long 0:05:01.560 --> 0:05:04.920 period of geologic time. If multiple groups of similar looking 0:05:04.960 --> 0:05:09.080 descendants independently evolved one after another from this common ancestor. 0:05:09.320 --> 0:05:12.000 It would be a clear cut case of iterative evolution. 0:05:13.200 --> 0:05:17.120 Consider the ammonites, spiral shelled relatives of squids and nautilus is. 0:05:17.320 --> 0:05:20.600 Ammonites roamed the oceans throughout the age of dinosaurs. Some 0:05:20.680 --> 0:05:23.880 experts think that individuals with thinner shells that were compressed 0:05:23.920 --> 0:05:26.760 from side to side were better suited for shallow environments 0:05:26.760 --> 0:05:30.000 with very fast currents. On the other hand, thicker, heavier 0:05:30.000 --> 0:05:33.039 shells nicely lent themselves too deep areas far off shore, 0:05:34.160 --> 0:05:36.760 So there's evidence that in certain parts of the world, 0:05:37.040 --> 0:05:40.400 an ancestral stock of thick shelled ammonites would periodically give 0:05:40.480 --> 0:05:44.400 rise to thin shelled descendants who invaded beachside habitats. When 0:05:44.440 --> 0:05:47.440 the sea levels fell, many of those habitats disappeared and 0:05:47.480 --> 0:05:51.400 the offshoot ammonites died out. But their thick shelled ancestors persisted, 0:05:51.640 --> 0:05:53.920 and when the oceans rose again, they'd sire a new 0:05:53.920 --> 0:05:58.240 generation of shallow water denizens with thin shells. And that's 0:05:58.240 --> 0:06:01.839 just one example. Innerative evolution might also explain the repeated 0:06:01.960 --> 0:06:04.160 rise and fall of similar looking sea cows over the 0:06:04.200 --> 0:06:08.120 past twenty six million years. Likewise, sea turtles, specifically the 0:06:08.160 --> 0:06:11.240 ones with seagrass centered diets, may have undergone the same 0:06:11.279 --> 0:06:15.520 process during their evolutionary history. While natural selection is a 0:06:15.520 --> 0:06:18.880 powerful force, cannot revive an extinct species, but when the 0:06:18.960 --> 0:06:21.360 environmental conditions are right, you can at least produce a 0:06:21.400 --> 0:06:29.320 good imitation. Today's episode was written by Mark Vancini and 0:06:29.360 --> 0:06:31.880 produced by Tyler Clang. Brain Stuff is a production of 0:06:31.920 --> 0:06:34.479 iHeart Radio's How Stuff Works. For more in this lots 0:06:34.480 --> 0:06:37.440 of other topics topics topics, visit our home planet, how 0:06:37.480 --> 0:06:39.960 stuff Works dot com. And for more podcasts for my 0:06:40.000 --> 0:06:42.960 heart Radio, visit the iHeart Radio app, Apple Podcasts, or 0:06:43.000 --> 0:06:44.560 wherever you listen to your favorite shows.