1 00:00:01,920 --> 00:00:07,120 Speaker 1: Welcome to brain Stuff production of iHeart Radio. Hey brain Stuff, 2 00:00:07,200 --> 00:00:10,559 Speaker 1: Lorn Vogel Bomb. Here out in the Indian Ocean, about 3 00:00:10,560 --> 00:00:13,039 Speaker 1: two hundred and fifty miles or four hundred kilometers to 4 00:00:13,039 --> 00:00:16,400 Speaker 1: the northwest of Madagascar, there's a shallow lagoon encircled by 5 00:00:16,400 --> 00:00:19,959 Speaker 1: a ring of islands. Those outcrops make up the Aldabra Atoll, 6 00:00:20,200 --> 00:00:22,960 Speaker 1: a place where mangroves flourish and one hundred thousand giant 7 00:00:23,000 --> 00:00:27,520 Speaker 1: tortoises roam free. Recently, a different resident caught the world's attention. 8 00:00:27,920 --> 00:00:30,920 Speaker 1: The Aldabra rail is a chicken sized bird found exclusively 9 00:00:30,960 --> 00:00:34,160 Speaker 1: on the atoll. It's also the only remaining island bird 10 00:00:34,200 --> 00:00:37,240 Speaker 1: in the Indian Ocean that happens to be flightless. Weak 11 00:00:37,360 --> 00:00:40,440 Speaker 1: arm muscles and asymmetrical flight feathers keep the bird grounded, 12 00:00:41,320 --> 00:00:45,080 Speaker 1: yet its ancestors could fly. The Aldabra rail evolved from 13 00:00:45,120 --> 00:00:47,520 Speaker 1: the white throated rail, a still living bird that flies 14 00:00:47,640 --> 00:00:51,199 Speaker 1: very well. Thank you. White throated rails inhabit Madagascar and 15 00:00:51,240 --> 00:00:54,160 Speaker 1: neighboring islands. Thousands of years ago, a number of these 16 00:00:54,200 --> 00:00:57,760 Speaker 1: birds flew out to the Aldabra Atoll. Then, as now, 17 00:00:58,120 --> 00:01:01,000 Speaker 1: large predators were rare on the atoll, but the thread 18 00:01:01,000 --> 00:01:04,120 Speaker 1: of predation mostly gone, the bird's descendants gradually lost the 19 00:01:04,160 --> 00:01:06,959 Speaker 1: ability to fly. That same thing happened to the dodo, 20 00:01:07,080 --> 00:01:11,400 Speaker 1: another island dwelling bird whose ancestors surrendered flight. Flying is 21 00:01:11,400 --> 00:01:13,959 Speaker 1: a high energy activity. When there's no need to fly 22 00:01:14,000 --> 00:01:16,400 Speaker 1: away from predators and you can get food simply by 23 00:01:16,400 --> 00:01:20,199 Speaker 1: walking around, why waste the energy on the Aldabra toll. 24 00:01:20,440 --> 00:01:24,920 Speaker 1: Flight became unnecessary for short term survival, So over many generations, 25 00:01:25,040 --> 00:01:28,000 Speaker 1: the isolated rail population gave rise to the fully flightless 26 00:01:28,040 --> 00:01:30,600 Speaker 1: birds we know today. But it turns out there's a 27 00:01:30,600 --> 00:01:34,000 Speaker 1: startling plot twist. Apparently the sequence of events we just 28 00:01:34,040 --> 00:01:38,000 Speaker 1: described happened more than once. A twenty nineteen studies suggests 29 00:01:38,040 --> 00:01:41,240 Speaker 1: that flighted colonizing rails came to Aldabra and begot a 30 00:01:41,280 --> 00:01:45,000 Speaker 1: non flying subspecies on two different occasions. It's as if 31 00:01:45,080 --> 00:01:49,040 Speaker 1: natural selection hit the reset button. Scientists call the phenomenon 32 00:01:49,160 --> 00:01:52,920 Speaker 1: iterative evolution. Today, we're going to explain what this process 33 00:01:53,040 --> 00:01:58,440 Speaker 1: entails and what it doesn't. University of Partsmith biologists Julian P. 34 00:01:58,680 --> 00:02:01,960 Speaker 1: Hume and David Martil co authored the groundbreaking new study, 35 00:02:02,160 --> 00:02:05,200 Speaker 1: which appeared in the Zoological Journal of the Linean Society. 36 00:02:05,520 --> 00:02:08,040 Speaker 1: Since their paper was published, Hume and Martell's work has 37 00:02:08,080 --> 00:02:11,360 Speaker 1: garnered a lot of press coverage. Unfortunately, their findings have 38 00:02:11,480 --> 00:02:15,000 Speaker 1: been widely misinterpreted. To hear, some media outlets tell it 39 00:02:15,280 --> 00:02:18,320 Speaker 1: the modern Aldabra rail went extinct and then resurrected itself 40 00:02:18,320 --> 00:02:20,680 Speaker 1: from the dead. But that's not what happened, and it's 41 00:02:20,760 --> 00:02:25,079 Speaker 1: not how iterative evolution works. Photographers love the Aldabra Toll 42 00:02:25,160 --> 00:02:28,600 Speaker 1: for its sunny beaches and blue lagoon. If you're a paleontologist, 43 00:02:28,720 --> 00:02:31,840 Speaker 1: the islands have another draw a bountiful fossil record going 44 00:02:31,880 --> 00:02:35,680 Speaker 1: back hundreds of thousands of years. On elate piccard the 45 00:02:35,680 --> 00:02:38,160 Speaker 1: westernmost island, a dig site has yielded a pair of 46 00:02:38,200 --> 00:02:42,440 Speaker 1: fossilized arm bones from prehistoric rails. Geologic clues tell us 47 00:02:42,480 --> 00:02:44,200 Speaker 1: the bones are more than a hundred and thirty six 48 00:02:44,200 --> 00:02:47,399 Speaker 1: thousand years old. It looks like the dead birds could 49 00:02:47,400 --> 00:02:50,560 Speaker 1: have used a good flood insurance policy. Judging by the 50 00:02:50,600 --> 00:02:54,480 Speaker 1: distribution of marine fossils like oceanic mollusk remains, it appears 51 00:02:54,480 --> 00:02:57,400 Speaker 1: the atoll was totally submerged under water multiple times in 52 00:02:57,400 --> 00:03:00,560 Speaker 1: the past four hundred thousand years. More we sently the 53 00:03:00,600 --> 00:03:03,079 Speaker 1: islands disappeared beneath the waves were about a hundred and 54 00:03:03,120 --> 00:03:05,880 Speaker 1: thirty six thousand to a hundred and eighteen thousand years 55 00:03:05,919 --> 00:03:09,600 Speaker 1: ago due to a rise in sea levels. Afterward, the 56 00:03:09,639 --> 00:03:13,040 Speaker 1: waters were treated and the atoll re emerged. And now 57 00:03:13,200 --> 00:03:16,560 Speaker 1: here's where the story takes an unexpected turn. The elip 58 00:03:16,680 --> 00:03:19,280 Speaker 1: card arm bones look almost identical to the ones we 59 00:03:19,320 --> 00:03:23,000 Speaker 1: see in living Aldabra rails today, which, as you'll recall, 60 00:03:23,040 --> 00:03:27,160 Speaker 1: are flightless. Therefore, the birds those fossils belonged to probably 61 00:03:27,160 --> 00:03:31,400 Speaker 1: couldn't fly either. So theoretically, when the atoll flooded, the 62 00:03:31,480 --> 00:03:34,520 Speaker 1: prehistoric rails in question were unable to escape and got 63 00:03:34,600 --> 00:03:38,640 Speaker 1: wiped out. However, the saga didn't end there. As human 64 00:03:38,720 --> 00:03:41,840 Speaker 1: Martel explain in their paper, the fossilized footbone of a 65 00:03:41,920 --> 00:03:44,800 Speaker 1: much more recent rail was once extracted from Grand Terror, 66 00:03:45,120 --> 00:03:48,360 Speaker 1: another island in the atoll. That specimen is only about 67 00:03:48,360 --> 00:03:51,560 Speaker 1: a hundred thousand years of age ergo its owner lived 68 00:03:51,600 --> 00:03:54,120 Speaker 1: after the sea levels went back down and the algebra 69 00:03:54,200 --> 00:03:58,320 Speaker 1: atoll resurfaced. In an intriguing case of deja vous, this 70 00:03:58,400 --> 00:04:01,760 Speaker 1: fossil closely resembles the bow in today's non flying Aldabra 71 00:04:01,920 --> 00:04:04,600 Speaker 1: rail and the assumption rail a bird that went extinct 72 00:04:04,600 --> 00:04:07,440 Speaker 1: in ninety seven. A primary sources indicate that it was 73 00:04:07,440 --> 00:04:11,200 Speaker 1: flightless too, but chances are the grand Terra fossil came 74 00:04:11,240 --> 00:04:13,240 Speaker 1: from a bird that either couldn't fly or was in 75 00:04:13,280 --> 00:04:16,479 Speaker 1: the process of losing its ability to do so. Either way, 76 00:04:16,520 --> 00:04:20,640 Speaker 1: it was the probable ancestor of modern aldebra rails. According 77 00:04:20,680 --> 00:04:23,520 Speaker 1: to human Martil, we're looking at an evolutionary do over. 78 00:04:24,000 --> 00:04:26,160 Speaker 1: The flightless birds that died out when the atoll went 79 00:04:26,240 --> 00:04:29,560 Speaker 1: under had descended from an ancestral stock of high soaring rails. 80 00:04:30,080 --> 00:04:32,760 Speaker 1: Once the islands vanished and then re emerged, those aerial 81 00:04:32,800 --> 00:04:36,120 Speaker 1: wanderers repopulated the atoll and evolved into an all new 82 00:04:36,240 --> 00:04:41,200 Speaker 1: flightless subspecies, one that's still at large today. History repeated 83 00:04:41,200 --> 00:04:45,040 Speaker 1: itself loud and clear, and that's iterative evolution and a nutshell. 84 00:04:46,200 --> 00:04:49,279 Speaker 1: Iterative evolution can be defined as the repeated evolution of 85 00:04:49,320 --> 00:04:52,160 Speaker 1: a specific trait or body plan from the same ancestral 86 00:04:52,160 --> 00:04:55,520 Speaker 1: lineage at different points in time. Let's say there's an 87 00:04:55,560 --> 00:04:58,359 Speaker 1: organism or a closely related group of organisms with a 88 00:04:58,400 --> 00:05:01,520 Speaker 1: fairly conservative build that manages to survive over a long 89 00:05:01,560 --> 00:05:04,920 Speaker 1: period of geologic time. If multiple groups of similar looking 90 00:05:04,960 --> 00:05:09,080 Speaker 1: descendants independently evolved one after another from this common ancestor. 91 00:05:09,320 --> 00:05:12,000 Speaker 1: It would be a clear cut case of iterative evolution. 92 00:05:13,200 --> 00:05:17,120 Speaker 1: Consider the ammonites, spiral shelled relatives of squids and nautilus is. 93 00:05:17,320 --> 00:05:20,600 Speaker 1: Ammonites roamed the oceans throughout the age of dinosaurs. Some 94 00:05:20,680 --> 00:05:23,880 Speaker 1: experts think that individuals with thinner shells that were compressed 95 00:05:23,920 --> 00:05:26,760 Speaker 1: from side to side were better suited for shallow environments 96 00:05:26,760 --> 00:05:30,000 Speaker 1: with very fast currents. On the other hand, thicker, heavier 97 00:05:30,000 --> 00:05:33,039 Speaker 1: shells nicely lent themselves too deep areas far off shore, 98 00:05:34,160 --> 00:05:36,760 Speaker 1: So there's evidence that in certain parts of the world, 99 00:05:37,040 --> 00:05:40,400 Speaker 1: an ancestral stock of thick shelled ammonites would periodically give 100 00:05:40,480 --> 00:05:44,400 Speaker 1: rise to thin shelled descendants who invaded beachside habitats. When 101 00:05:44,440 --> 00:05:47,440 Speaker 1: the sea levels fell, many of those habitats disappeared and 102 00:05:47,480 --> 00:05:51,400 Speaker 1: the offshoot ammonites died out. But their thick shelled ancestors persisted, 103 00:05:51,640 --> 00:05:53,920 Speaker 1: and when the oceans rose again, they'd sire a new 104 00:05:53,920 --> 00:05:58,240 Speaker 1: generation of shallow water denizens with thin shells. And that's 105 00:05:58,240 --> 00:06:01,839 Speaker 1: just one example. Innerative evolution might also explain the repeated 106 00:06:01,960 --> 00:06:04,160 Speaker 1: rise and fall of similar looking sea cows over the 107 00:06:04,200 --> 00:06:08,120 Speaker 1: past twenty six million years. Likewise, sea turtles, specifically the 108 00:06:08,160 --> 00:06:11,240 Speaker 1: ones with seagrass centered diets, may have undergone the same 109 00:06:11,279 --> 00:06:15,520 Speaker 1: process during their evolutionary history. While natural selection is a 110 00:06:15,520 --> 00:06:18,880 Speaker 1: powerful force, cannot revive an extinct species, but when the 111 00:06:18,960 --> 00:06:21,360 Speaker 1: environmental conditions are right, you can at least produce a 112 00:06:21,400 --> 00:06:29,320 Speaker 1: good imitation. Today's episode was written by Mark Vancini and 113 00:06:29,360 --> 00:06:31,880 Speaker 1: produced by Tyler Clang. Brain Stuff is a production of 114 00:06:31,920 --> 00:06:34,479 Speaker 1: iHeart Radio's How Stuff Works. For more in this lots 115 00:06:34,480 --> 00:06:37,440 Speaker 1: of other topics topics topics, visit our home planet, how 116 00:06:37,480 --> 00:06:39,960 Speaker 1: stuff Works dot com. And for more podcasts for my 117 00:06:40,000 --> 00:06:42,960 Speaker 1: heart Radio, visit the iHeart Radio app, Apple Podcasts, or 118 00:06:43,000 --> 00:06:44,560 Speaker 1: wherever you listen to your favorite shows.