WEBVTT 1 00:00:19.834 --> 00:00:23.367 [NARRATOR:] Our planet has millions of species. 2 00:00:23.367 --> 00:00:27.334 Over 300,000 beetles alone. 3 00:00:27.334 --> 00:00:31.033 17,000 butterflies. 4 00:00:31.033 --> 00:00:33.701 Thousands of mammals, fish and birds, 5 00:00:33.701 --> 00:00:36.334 all astonishingly different. 6 00:00:40.067 --> 00:00:43.701 How did so many species come to be? 7 00:00:47.667 --> 00:00:50.300 To seek insights into that question, 8 00:00:50.300 --> 00:00:52.267 researchers are focusing on places 9 00:00:52.267 --> 00:00:55.000 where species recently arose, 10 00:00:55.000 --> 00:00:58.634 such as the remote Galápagos Islands. 11 00:00:58.634 --> 00:01:00.267 [CARROLL:] Scientists are making observations 12 00:01:00.267 --> 00:01:01.767 and conducting experiments 13 00:01:01.767 --> 00:01:03.267 that would have surprised Charles Darwin. 14 00:01:04.934 --> 00:01:06.334 And they're discovering new insights 15 00:01:06.334 --> 00:01:09.601 into what the great naturalist called the "mystery of mysteries": 16 00:01:10.434 --> 00:01:12.334 How new species form. 17 00:01:22.000 --> 00:01:23.901 [NARRATOR:] The Galápagos Islands are one 18 00:01:23.901 --> 00:01:27.767 of the most spectacular landscapes in the world, 19 00:01:27.767 --> 00:01:32.167 home to a variety of species that live nowhere else. 20 00:01:36.267 --> 00:01:39.968 Biologists Peter and Rosemary Grant have been seeking answers 21 00:01:39.968 --> 00:01:42.567 to how species arise by focusing on one 22 00:01:42.567 --> 00:01:46.267 of the smaller islands, called Daphne Major. 23 00:01:51.167 --> 00:01:53.033 [PETER GRANT:] When we started out, we had 24 00:01:53.033 --> 00:01:56.767 no plan for the long term. 25 00:01:56.767 --> 00:01:57.934 In fact, we thought it was just going 26 00:01:57.934 --> 00:02:01.634 to be just a few years, maybe two years. 27 00:02:01.634 --> 00:02:05.834 [NARRATOR:] Two years have turned into a 40-year odyssey. 28 00:02:05.834 --> 00:02:09.200 The Grants have returned every summer since 1973. 29 00:02:09.200 --> 00:02:10.167 [ROSEMARY GRANT:] Oh, there's a bird. 30 00:02:10.167 --> 00:02:12.167 [PETER GRANT:] Is that 306? 31 00:02:12.167 --> 00:02:14.033 [ROSEMARY GRANT:] Three oh metal six. 32 00:02:14.033 --> 00:02:15.434 [NARRATOR:] Here, they've made some 33 00:02:15.434 --> 00:02:18.067 of the most remarkable observations in the history 34 00:02:18.067 --> 00:02:21.901 of field research as they studied the famed 35 00:02:21.901 --> 00:02:24.133 Galápagos finches. 36 00:02:31.334 --> 00:02:33.601 The finches were first brought to scientists' attention 37 00:02:33.601 --> 00:02:37.434 by Charles Darwin, when his voyage 38 00:02:37.434 --> 00:02:39.801 around South America brought him to this cluster 39 00:02:39.801 --> 00:02:44.200 of islands 600 miles from mainland Ecuador. 40 00:02:48.767 --> 00:02:52.901 These volcanic islands are geologically young. 41 00:02:52.901 --> 00:02:55.000 They began rising from the ocean floor less 42 00:02:55.000 --> 00:02:56.534 than five million years ago. 43 00:02:57.234 --> 00:02:59.968 At first devoid of life, 44 00:02:59.968 --> 00:03:03.501 they now support a modest number of species. 45 00:03:08.033 --> 00:03:11.501 Among them, 13 species of finches found 46 00:03:11.501 --> 00:03:14.934 in various combinations on the different islands. 47 00:03:16.834 --> 00:03:19.501 The birds live in diverse habitats. 48 00:03:21.067 --> 00:03:22.968 [ROSEMARY GRANT:] The islands are very different 49 00:03:22.968 --> 00:03:23.734 from each other. 50 00:03:23.734 --> 00:03:24.968 They differ in size. 51 00:03:24.968 --> 00:03:28.834 They differ in topography and in height. 52 00:03:31.968 --> 00:03:33.367 [NARRATOR:] Larger trees grow 53 00:03:33.367 --> 00:03:37.400 at higher elevations while low islands have mostly cactus, 54 00:03:37.400 --> 00:03:40.033 grasses and shrubs. 55 00:03:42.467 --> 00:03:44.567 In these diverse habitats, 56 00:03:44.567 --> 00:03:48.133 the finches have evolved many ways to survive. 57 00:03:49.334 --> 00:03:50.601 [CARROLL:] So Rosemary, 58 00:03:50.601 --> 00:03:52.934 what's the important difference between these birds? 59 00:03:52.934 --> 00:03:54.334 [ROSEMARY GRANT:] This little warbler finch 60 00:03:54.334 --> 00:03:58.100 with its very fine needlelike beak is perfect 61 00:03:58.100 --> 00:04:01.567 for picking off insects. 62 00:04:01.567 --> 00:04:07.667 This one is the woodpecker finch with a rather more robust beak. 63 00:04:07.667 --> 00:04:12.767 It concentrates on beetle larvae and termite larvae. 64 00:04:14.334 --> 00:04:17.801 Then we have the cactus finch 65 00:04:17.801 --> 00:04:19.834 with a much longer sharp pointed beak 66 00:04:19.834 --> 00:04:23.033 which probes into cactus flowers. 67 00:04:23.033 --> 00:04:26.067 And then these three species are the large, 68 00:04:26.067 --> 00:04:29.734 medium and small ground finches. 69 00:04:29.734 --> 00:04:33.501 So, Sean, a basic idea is, the beaks are tools 70 00:04:33.501 --> 00:04:36.601 and you need the right tool for the right job. 71 00:04:40.234 --> 00:04:42.601 [NARRATOR:] The finches look so different 72 00:04:42.601 --> 00:04:44.634 that Darwin first mistook them 73 00:04:44.634 --> 00:04:48.400 for entirely unrelated kinds of birds. 74 00:04:48.400 --> 00:04:53.300 How did the Galápagos end up with so many species of finches? 75 00:04:54.400 --> 00:04:57.434 [CARROLL:] In terms of the actual history of the finches 76 00:04:57.434 --> 00:05:02.133 of the Galápagos, there were many different possibilities. 77 00:05:02.133 --> 00:05:03.901 Different kinds of finches could have all come 78 00:05:03.901 --> 00:05:07.234 from the mainland separately 79 00:05:07.234 --> 00:05:08.968 or the finches could have all evolved 80 00:05:08.968 --> 00:05:11.100 out there on the islands. 81 00:05:12.300 --> 00:05:15.267 And what do we know about that? 82 00:05:15.267 --> 00:05:19.534 [PETER GRANT:] Well, now we know from DNA evidence that all 83 00:05:19.534 --> 00:05:23.601 of the finches are more related to each other than any one is 84 00:05:23.601 --> 00:05:26.501 to a species on the mainland. 85 00:05:26.501 --> 00:05:29.400 And that tells us only one species arrived 86 00:05:29.400 --> 00:05:33.734 on the archipelago, and diversified into the 13 species 87 00:05:33.734 --> 00:05:35.801 that we see nowadays in the Galápagos. 88 00:05:35.801 --> 00:05:41.300 So they've all come from a single common ancestor. 89 00:05:45.234 --> 00:05:48.601 [NARRATOR:] The question then becomes how did one ancestral 90 00:05:48.601 --> 00:05:53.601 population give rise to many different species, each adapted 91 00:05:53.601 --> 00:05:55.934 to a different lifestyle. 92 00:05:59.200 --> 00:06:02.734 A crucial insight into how adaptation occurs came 93 00:06:02.734 --> 00:06:05.400 when the Grants focused on one species 94 00:06:05.400 --> 00:06:09.033 on the island of Daphne Major. 95 00:06:09.033 --> 00:06:10.634 [PETER GRANT:] Factor of great convenience 96 00:06:10.634 --> 00:06:14.467 for us was the small size of the island. 97 00:06:14.467 --> 00:06:17.801 That meant that we could walk all over the place. 98 00:06:19.467 --> 00:06:22.234 [ROSEMARY GRANT:] The idea was that if we worked really hard, 99 00:06:22.234 --> 00:06:26.667 we could follow every individual or almost every individual. 100 00:06:27.801 --> 00:06:30.267 [NARRATOR:] They rose at 5:30 each morning 101 00:06:30.267 --> 00:06:33.567 to net the island's medium ground finches. 102 00:06:37.934 --> 00:06:39.767 [NARRATOR:] They measured the size and shape 103 00:06:39.767 --> 00:06:43.200 of each bird's beak, the bird's weight 104 00:06:43.200 --> 00:06:46.534 and they tagged them for identification. 105 00:06:50.834 --> 00:06:52.868 [NARRATOR:] Year after year they returned, 106 00:06:52.868 --> 00:06:55.767 at times tracking over 1,000 finches. 107 00:06:58.667 --> 00:07:00.501 [PETER GRANT:] So here's an example 108 00:07:00.501 --> 00:07:04.300 of a bird we know intimately over the whole of its lifespan. 109 00:07:04.300 --> 00:07:06.734 The number is 5960. 110 00:07:06.734 --> 00:07:10.234 We know how many times it bred, which years it bred in, 111 00:07:10.234 --> 00:07:14.067 how many mates it had, how many offspring it produced. 112 00:07:14.067 --> 00:07:17.501 And then how many of those offspring themselves survived 113 00:07:17.501 --> 00:07:18.901 long enough to breed. 114 00:07:20.334 --> 00:07:24.501 [NARRATOR:] Over the first four years, little seemed to change. 115 00:07:26.100 --> 00:07:31.467 Then in 1977 a terrible drought began. 116 00:07:31.467 --> 00:07:34.868 [PETER GRANT:] Virtually no rain fell for the next 18 months. 117 00:07:34.868 --> 00:07:38.367 [ROSEMARY GRANT:] The vegetation practically disappeared apart 118 00:07:38.367 --> 00:07:40.400 from a few trees without any leaves. 119 00:07:40.400 --> 00:07:44.434 And, of course, the cactus bushes were still there. 120 00:07:47.033 --> 00:07:49.300 [NARRATOR:] Now the medium ground finches had 121 00:07:49.300 --> 00:07:52.267 to compete for scarce food. 122 00:07:52.267 --> 00:07:54.767 [PETER GRANT:] They started off with a big food supply 123 00:07:54.767 --> 00:07:57.667 of small seeds, medium seeds, large seeds. 124 00:07:57.667 --> 00:08:00.901 As these small seeds became very scarce, 125 00:08:00.901 --> 00:08:04.701 they had to turn increasingly to the large and hard seeds. 126 00:08:04.701 --> 00:08:07.667 Well, only birds with large beaks can crack open these 127 00:08:07.667 --> 00:08:10.868 woody, spiny fruits. 128 00:08:15.701 --> 00:08:17.868 [NARRATOR:] The birds with the smallest beaks had the 129 00:08:17.868 --> 00:08:19.534 most trouble. 130 00:08:19.534 --> 00:08:20.501 [ROSEMARY GRANT:] They were scraping 131 00:08:20.501 --> 00:08:25.701 about amongst the rocks, and their plumage got so worn 132 00:08:25.701 --> 00:08:28.601 that they could barely fly. 133 00:08:30.067 --> 00:08:32.868 [NARRATOR:] That year, over 80 percent 134 00:08:32.868 --> 00:08:35.300 of the medium ground finches died. 135 00:08:36.300 --> 00:08:37.834 [PETER GRANT:] We would go around looking 136 00:08:37.834 --> 00:08:39.901 for birds that had died. 137 00:08:39.901 --> 00:08:44.734 And it's very sad to pick up a bird and say, "3972. 138 00:08:44.734 --> 00:08:46.000 "Oh no, not that bird. 139 00:08:46.000 --> 00:08:46.834 "Oh." 140 00:08:48.567 --> 00:08:52.200 [NARRATOR:] When they inventoried the surviving medium 141 00:08:52.200 --> 00:08:54.300 ground finches, they discovered 142 00:08:54.300 --> 00:08:57.133 that one trait had made the greatest difference 143 00:08:57.133 --> 00:08:59.701 between life and death. 144 00:08:59.701 --> 00:09:01.601 [PETER GRANT:] What I'm showing here, a distribution 145 00:09:01.601 --> 00:09:05.534 of beak depths of the population in 1976. 146 00:09:06.534 --> 00:09:10.801 The survivors of this group are shown in black. 147 00:09:10.801 --> 00:09:11.767 [CARROLL:] Oh. 148 00:09:11.767 --> 00:09:13.834 So the larger the beak, the better your chances? 149 00:09:13.834 --> 00:09:16.367 [PETER GRANT:] The larger the beak, the higher the likelihood 150 00:09:16.367 --> 00:09:20.200 of surviving through the drought of 1977. 151 00:09:21.100 --> 00:09:24.167 [PETER GRANT:] 18.6 grams. 152 00:09:24.167 --> 00:09:25.934 [NARRATOR:] When they looked at the offspring, 153 00:09:25.934 --> 00:09:28.834 they found an even greater surprise. 154 00:09:28.834 --> 00:09:31.934 The average beak depth was more than four percent larger 155 00:09:31.934 --> 00:09:35.067 than the previous generation. 156 00:09:35.067 --> 00:09:40.534 Natural selection had changed the average beak size. 157 00:09:40.868 --> 00:09:44.133 [CARROLL:] Could you have ever imagined measuring 158 00:09:44.133 --> 00:09:47.734 and observing something like this on such a short time scale 159 00:09:47.734 --> 00:09:49.033 until you actually did it? 160 00:09:49.033 --> 00:09:51.400 [PETER GRANT:] When we started, the answer is no. 161 00:09:51.400 --> 00:09:53.834 We could not imagine we would be able to do it. 162 00:09:55.367 --> 00:09:58.334 [NARRATOR:] But was this a fluke? 163 00:09:58.334 --> 00:10:03.033 Or are changes like this happening all the time? 164 00:10:03.033 --> 00:10:05.968 Five years later in 1983, 165 00:10:05.968 --> 00:10:09.667 an unusually strong El Nino brought ten times more rain 166 00:10:09.667 --> 00:10:11.667 than normal. 167 00:10:11.868 --> 00:10:15.334 And the island was overrun by vines 168 00:10:15.334 --> 00:10:17.434 that covered even the cactus. 169 00:10:18.400 --> 00:10:22.133 The rains changed the vegetation on the island, 170 00:10:22.133 --> 00:10:25.834 such that two years later, when drought struck, 171 00:10:25.834 --> 00:10:28.634 larger seeds became scarce. 172 00:10:30.367 --> 00:10:33.934 The birds with larger beaks now had difficulty picking 173 00:10:33.934 --> 00:10:36.133 up the more abundant food: 174 00:10:36.133 --> 00:10:39.734 the small seeds produced by the vines. 175 00:10:41.300 --> 00:10:44.434 That year many more finches with small beaks survived, 176 00:10:44.434 --> 00:10:49.234 and their offspring inherited smaller beaks. 177 00:10:50.601 --> 00:10:52.601 [PETER GRANT:] So the selection had swung 178 00:10:52.601 --> 00:10:54.000 in the opposite direction, 179 00:10:54.000 --> 00:10:56.667 and evolution had occurred as a result. 180 00:10:58.667 --> 00:11:01.534 [CARROLL:] In an amazingly short period of time, 181 00:11:01.534 --> 00:11:03.968 the Grants had measured evolution of beak size, 182 00:11:03.968 --> 00:11:06.767 not once, but twice, demonstrating 183 00:11:06.767 --> 00:11:09.300 that when birds encounter different environments they will 184 00:11:09.300 --> 00:11:13.667 change over a very short amount of time. 185 00:11:13.667 --> 00:11:15.667 [NARRATOR:] Over millions of years, 186 00:11:15.667 --> 00:11:19.300 changes like these occurring throughout the Galápagos 187 00:11:19.300 --> 00:11:22.000 generated all sorts of beak sizes and shapes. 188 00:11:23.667 --> 00:11:26.200 But that's only part of the story. 189 00:11:26.200 --> 00:11:30.868 How did finches with different beaks become distinct species? 190 00:11:32.334 --> 00:11:34.033 Species are defined 191 00:11:34.033 --> 00:11:37.067 as populations whose members don't interbreed. 192 00:11:38.067 --> 00:11:41.167 [CARROLL:] So how does one species split into two? 193 00:11:41.167 --> 00:11:44.868 A typical scenario is that two populations become separated 194 00:11:44.868 --> 00:11:47.534 geographically, and undergo enough change 195 00:11:47.534 --> 00:11:50.267 in their respective habitats, that if or when they come 196 00:11:50.267 --> 00:11:52.801 into contact again, they do not mate. 197 00:11:55.133 --> 00:11:56.968 [NARRATOR:] So in the Galápagos, 198 00:11:56.968 --> 00:11:59.868 the Grants asked what keeps different species 199 00:11:59.868 --> 00:12:03.133 of finches from mating? 200 00:12:03.133 --> 00:12:04.534 [ROSEMARY GRANT:] We were very conscious 201 00:12:04.534 --> 00:12:06.467 that on any given island, 202 00:12:06.467 --> 00:12:11.734 the different species sing very different songs. 203 00:12:11.734 --> 00:12:14.501 This is what a cactus finch sounds like. 204 00:12:14.501 --> 00:12:16.868 [chirping] 205 00:12:16.868 --> 00:12:23.367 Whereas the medium ground finch sounds very much 206 00:12:23.367 --> 00:12:24.901 like this. 207 00:12:24.901 --> 00:12:27.434 [chirping] 208 00:12:30.267 --> 00:12:32.968 [NARRATOR:] So to see if songs keep the species apart, 209 00:12:32.968 --> 00:12:36.400 the Grants, and their student Laurene Ratcliffe, 210 00:12:36.400 --> 00:12:40.200 played each species' songs through a loudspeaker. 211 00:12:42.634 --> 00:12:46.534 [ROSEMARY GRANT:] When we played back the cactus finch song, 212 00:12:46.534 --> 00:12:48.300 cactus finch came to the loudspeaker 213 00:12:48.300 --> 00:12:53.667 and the medium ground finch completely ignored it. 214 00:12:53.667 --> 00:12:55.801 [NARRATOR:] The males only responded 215 00:12:55.801 --> 00:12:58.901 to songs of their own species. 216 00:13:00.667 --> 00:13:03.968 The Grants looked at whether finches might also choose mates 217 00:13:03.968 --> 00:13:05.634 based on appearance. 218 00:13:07.534 --> 00:13:10.567 So they put out stuffed female specimens to see 219 00:13:10.567 --> 00:13:12.434 if males would respond. 220 00:13:14.934 --> 00:13:16.968 [ROSEMARY GRANT:] Clearly they could discriminate. 221 00:13:16.968 --> 00:13:21.133 The male vigorously courted a female of his own species; 222 00:13:21.133 --> 00:13:22.767 completely ignored the other one. 223 00:13:24.934 --> 00:13:26.934 [NARRATOR:] The males only courted females 224 00:13:26.934 --> 00:13:30.901 that had a similar size and similar beak. 225 00:13:30.901 --> 00:13:33.601 Song and appearance both play a role 226 00:13:33.601 --> 00:13:36.501 in keeping different species from mating. 227 00:13:37.901 --> 00:13:41.701 So when populations of the same species are separated, 228 00:13:41.701 --> 00:13:44.334 changes in these traits set the stage 229 00:13:44.334 --> 00:13:47.801 for the formation of new species. 230 00:13:49.367 --> 00:13:54.434 The Grants have shown that both geography and ecology are keys 231 00:13:54.434 --> 00:13:57.667 to the evolution of the Galápagos finches. 232 00:14:00.434 --> 00:14:04.267 The most likely scenario is that, two million years ago, 233 00:14:04.267 --> 00:14:08.067 a single finch population arrived from the mainland. 234 00:14:11.334 --> 00:14:13.601 When their descendants reached another island, 235 00:14:13.601 --> 00:14:15.167 they faced new conditions. 236 00:14:15.167 --> 00:14:19.000 As those isolated populations adapted 237 00:14:19.000 --> 00:14:24.100 to their surroundings, their traits changed. 238 00:14:24.100 --> 00:14:26.801 If the changes included traits involved in mating, 239 00:14:26.801 --> 00:14:28.934 and the populations came 240 00:14:28.934 --> 00:14:33.267 into contact again, they no longer mated. 241 00:14:33.267 --> 00:14:36.868 They had become distinct species. 242 00:14:40.934 --> 00:14:43.400 While unique to these remote islands, 243 00:14:43.400 --> 00:14:47.634 the history of the Galápagos finches offers a general insight 244 00:14:47.634 --> 00:14:53.367 into why the world is populated with so many species. 245 00:14:53.367 --> 00:14:55.667 [PETER GRANT:] The more diverse the environment, 246 00:14:55.667 --> 00:14:58.567 the more opportunities for evolutionary change 247 00:14:58.567 --> 00:15:01.234 to produce those new species. 248 00:15:05.968 --> 00:15:07.901 [NARRATOR:] Over 150 years 249 00:15:07.901 --> 00:15:10.868 after Darwin first recognized their significance, 250 00:15:10.868 --> 00:15:14.267 these unassuming birds still illuminate how the great 251 00:15:14.267 --> 00:15:18.501 diversity of life arose and continues to evolve.