1 00:00:04,571 --> 00:00:10,577 MAN: It's a basic human need to ask, "Who are we?" 2 00:00:12,078 --> 00:00:13,580 "Where do we come from?" 3 00:00:15,081 --> 00:00:17,083 "How did we get here?" 4 00:00:17,083 --> 00:00:20,086 "Why do we look the way we do?" 5 00:00:23,590 --> 00:00:25,592 NARRATOR: The story of our evolution 6 00:00:25,592 --> 00:00:28,595 is just a small chapter in a much larger story: 7 00:00:28,595 --> 00:00:32,599 the evolution of all living things. 8 00:00:32,599 --> 00:00:34,601 (trumpeting) 9 00:00:34,601 --> 00:00:37,604 MAN: Evolution shows us that we're much more connected 10 00:00:37,604 --> 00:00:40,607 to the rest of the world, the rest of animal life 11 00:00:40,607 --> 00:00:42,609 than we could ever have imagined. 12 00:00:42,609 --> 00:00:46,613 NARRATOR: We can recognize the connection to our closest relatives 13 00:00:46,613 --> 00:00:49,115 but when we know how to look 14 00:00:49,115 --> 00:00:52,118 we can also find it in other mammals: 15 00:00:52,118 --> 00:00:53,620 birds... 16 00:00:53,620 --> 00:00:55,121 reptiles... 17 00:00:55,121 --> 00:00:57,123 fish... 18 00:00:57,123 --> 00:00:59,626 even insects. 19 00:01:01,628 --> 00:01:05,131 The deeper we dig, the farther back we go 20 00:01:05,131 --> 00:01:08,635 the more we see that everything alive has evolved 21 00:01:08,635 --> 00:01:10,637 from a single starting point. 22 00:01:12,138 --> 00:01:14,140 The tree of life has been branching 23 00:01:14,140 --> 00:01:16,142 for four billion years. 24 00:01:18,645 --> 00:01:22,148 And we can now follow its branches back to their roots. 25 00:01:22,148 --> 00:01:24,651 MAN: When we look back over time 26 00:01:24,651 --> 00:01:27,654 we find certain signposts, certain key events 27 00:01:27,654 --> 00:01:31,157 the great transformations, the big evolutionary steps. 28 00:01:31,157 --> 00:01:35,662 NARRATOR: In the history of our planet, a few great transformations 29 00:01:35,662 --> 00:01:38,665 have opened the door for new ways of life 30 00:01:38,665 --> 00:01:41,167 and new forms of life. 31 00:01:43,169 --> 00:01:45,171 50 million years ago 32 00:01:45,171 --> 00:01:49,175 land mammals evolved into sea creatures. 33 00:01:49,175 --> 00:01:53,179 Long before that, fish colonized land. 34 00:01:55,181 --> 00:01:58,184 At the dawn of animal life itself 35 00:01:58,685 --> 00:02:01,187 the first bodies appeared. 36 00:02:01,187 --> 00:02:07,193 These are some of the chapters in life's story... our story. 37 00:02:08,695 --> 00:02:11,698 MAN: And... and part of the fun of studying this 38 00:02:11,698 --> 00:02:14,200 is understanding each different chapter 39 00:02:14,200 --> 00:02:16,202 because by understanding those chapters 40 00:02:16,202 --> 00:02:18,705 we can begin to see the unity of life, 41 00:02:18,705 --> 00:02:20,707 the common history of all life on Earth. 42 00:03:01,247 --> 00:03:05,752 NARRATOR: Human civilization stretches back thousands of years. 43 00:03:07,754 --> 00:03:11,257 But compared to the age of the earth 44 00:03:11,257 --> 00:03:14,260 we humans have only just arrived. 45 00:03:14,260 --> 00:03:17,263 MAN: The earth is really old. 46 00:03:17,263 --> 00:03:19,265 If you take the entire history of the earth 47 00:03:19,265 --> 00:03:21,768 from 4.6 billion years ago to the present 48 00:03:21,768 --> 00:03:23,770 and sort of call that an hour... 49 00:03:24,270 --> 00:03:25,772 (clock chime dings) 50 00:03:25,772 --> 00:03:29,275 SHUBIN: The first 50 minutes are largely spent 51 00:03:29,275 --> 00:03:33,279 in a world of microbes, single-celled organisms. 52 00:03:33,279 --> 00:03:35,281 (clock ticking) 53 00:03:35,281 --> 00:03:38,785 Animal life appeared in the last ten minutes of that hour. 54 00:03:38,785 --> 00:03:40,787 (clock ticking) 55 00:03:40,787 --> 00:03:44,791 All of human history, our civilization, our evolution, 56 00:03:44,791 --> 00:03:48,795 happened in the last hundredth of a second of that hour. 57 00:03:48,795 --> 00:03:50,797 (clock chime dings) 58 00:03:50,797 --> 00:03:52,799 CHILDREN: ? Ring-around-a-rosy... ? 59 00:03:52,799 --> 00:03:55,301 NARRATOR: We've come quite late to the party 60 00:03:55,301 --> 00:03:57,804 but we've been shaped by the same forces 61 00:03:57,804 --> 00:04:00,306 that have helped shape all life on Earth. 62 00:04:00,306 --> 00:04:03,309 CHILDREN: ? ...We all fall down. ? 63 00:04:03,309 --> 00:04:07,313 NARRATOR: To understand how we fit in, we need to look back 64 00:04:07,313 --> 00:04:09,315 to long before our own origins 65 00:04:09,315 --> 00:04:11,818 to see how other living things evolved. 66 00:04:12,819 --> 00:04:15,822 (whales singing) 67 00:04:15,822 --> 00:04:18,825 NARRATOR: Whales are the largest living animals. 68 00:04:18,825 --> 00:04:22,328 Like us, whales and dolphins 69 00:04:22,829 --> 00:04:25,331 took on their present forms relatively recently. 70 00:04:26,833 --> 00:04:30,336 For a long time, the origin of these marine mammals 71 00:04:30,336 --> 00:04:31,838 was a scientific mystery. 72 00:04:31,838 --> 00:04:35,341 MAN: Whales are so different from every other kind of mammal 73 00:04:35,341 --> 00:04:38,845 that we can't easily relate them to anything else 74 00:04:38,845 --> 00:04:43,349 and so they're off by themself as a branch of mammal evolution. 75 00:04:43,349 --> 00:04:48,354 NARRATOR: Mammals first appeared on Earth around 200 million years ago... 76 00:04:48,354 --> 00:04:50,356 on land. 77 00:04:50,356 --> 00:04:53,359 Mammals are warm-blooded 78 00:04:53,359 --> 00:04:59,866 they give birth to living young and they breathe air. 79 00:04:59,866 --> 00:05:03,870 These are all adaptations to living on land. 80 00:05:06,873 --> 00:05:08,374 (dolphin clicking) 81 00:05:08,374 --> 00:05:11,878 NARRATOR: But whales and dolphins are mammals, too. 82 00:05:11,878 --> 00:05:15,381 SHUBIN: They're mammals that live in the water 83 00:05:15,381 --> 00:05:18,885 but we know that mammals evolved on land. 84 00:05:18,885 --> 00:05:23,389 So it's a real puzzle how whales originally evolved. 85 00:05:23,890 --> 00:05:25,892 By understanding how that happens 86 00:05:25,892 --> 00:05:28,895 we'll begin to understand how these big jumps 87 00:05:28,895 --> 00:05:31,898 these big transformations happen generally. 88 00:05:33,900 --> 00:05:36,903 GINGERICH: People are interested in whales, and I can understand. 89 00:05:36,903 --> 00:05:39,405 They're so beautiful. 90 00:05:39,405 --> 00:05:42,909 Their origin is such a mystery. 91 00:05:42,909 --> 00:05:45,912 Whales are one of the few groups of mammals 92 00:05:46,412 --> 00:05:49,916 that have really large, complicated brains like we do. 93 00:05:49,916 --> 00:05:54,420 And so in a sense, they're our alter egos living in the sea 94 00:05:54,420 --> 00:05:55,922 while we live on land 95 00:05:55,922 --> 00:05:58,925 dominating the sea while we dominate land. 96 00:05:58,925 --> 00:06:00,426 And I think for that reason 97 00:06:00,426 --> 00:06:03,429 we're very interested in what goes on there 98 00:06:03,429 --> 00:06:06,933 how they got there, as a reflection of our own history 99 00:06:06,933 --> 00:06:08,935 through geological time. 100 00:06:10,436 --> 00:06:14,440 NARRATOR: When Phil Gingerich began his career 30 years ago 101 00:06:14,440 --> 00:06:18,444 he knew nothing about whales, and that was just fine with him. 102 00:06:19,946 --> 00:06:22,949 He was drawn to geology mostly because 103 00:06:22,949 --> 00:06:26,452 he couldn't imagine a career spent behind a desk. 104 00:06:26,452 --> 00:06:28,955 GINGERICH: I think I was interested in geology 105 00:06:28,955 --> 00:06:30,957 because it was a science outdoors. 106 00:06:30,957 --> 00:06:34,460 And in geology, I became interested in paleontology 107 00:06:34,460 --> 00:06:37,964 because it was about life and the history of life. 108 00:06:37,964 --> 00:06:40,967 NARRATOR: Gingerich's early interest in primitive land mammals 109 00:06:40,967 --> 00:06:44,470 eventually took him to Pakistan. 110 00:06:46,973 --> 00:06:49,976 It was there that he made the kind of find 111 00:06:49,976 --> 00:06:52,979 most paleontologists only dream about: 112 00:06:52,979 --> 00:06:57,483 a fossil that would rewrite one of evolution's greatest stories. 113 00:06:57,483 --> 00:07:01,988 GINGERICH: I found the back of a skull that I couldn't identify. 114 00:07:01,988 --> 00:07:04,991 It had a very good, well-preserved ear region 115 00:07:04,991 --> 00:07:07,493 and that offered the clue to what it was. 116 00:07:08,995 --> 00:07:11,497 NARRATOR: The shape was familiar 117 00:07:11,497 --> 00:07:16,002 but in other ways it was like nothing Gingerich had ever seen. 118 00:07:16,002 --> 00:07:18,004 This is the original specimen. 119 00:07:18,004 --> 00:07:20,006 It's the one we found in about 1978. 120 00:07:20,006 --> 00:07:22,008 There's several things that strike you. 121 00:07:22,008 --> 00:07:24,010 One is it's very similar in size and shape 122 00:07:24,010 --> 00:07:27,013 to the back of a skull of a wolf. 123 00:07:28,514 --> 00:07:31,517 NARRATOR: But there was something odd about this skull. 124 00:07:33,019 --> 00:07:36,022 On its underside was a walnut-sized bump. 125 00:07:36,022 --> 00:07:38,024 GINGERICH: If this wasn't here 126 00:07:38,024 --> 00:07:42,028 I would think that this was an archaic carnivorous mammal 127 00:07:42,028 --> 00:07:45,031 or what we call a creodont, but it is here. 128 00:07:46,532 --> 00:07:49,035 NARRATOR: It was part of the animal's inner ear 129 00:07:49,035 --> 00:07:51,537 and it had a distinctive shape, 130 00:07:51,537 --> 00:07:59,045 a shape found today in only one kind of animal: whales. 131 00:08:00,546 --> 00:08:04,550 What was the ear of a whale doing on the skull of an animal 132 00:08:04,550 --> 00:08:06,552 that resembled a wolf? 133 00:08:09,055 --> 00:08:13,059 Gingerich was intrigued, so he constructed a model 134 00:08:13,059 --> 00:08:18,064 of what the creature's full skull might have looked like. 135 00:08:18,064 --> 00:08:22,068 He wondered, was his find a crucial missing link 136 00:08:22,068 --> 00:08:25,071 the first fossil evidence ever found 137 00:08:25,071 --> 00:08:28,074 for one of Darwin's most daring claims, 138 00:08:28,074 --> 00:08:32,078 that whales had evolved from land mammals? 139 00:08:35,081 --> 00:08:36,582 To know for sure 140 00:08:36,582 --> 00:08:39,085 Gingerich would need to find more fossils... 141 00:08:41,087 --> 00:08:46,592 ones that would show each stage of the whale transformation, 142 00:08:46,592 --> 00:08:51,097 what scientists call "transitional forms." 143 00:08:51,097 --> 00:08:52,598 I want to line them all up. 144 00:08:52,598 --> 00:08:54,600 I want anyone to be able to see it 145 00:08:54,600 --> 00:08:57,103 and believe it because they've seen it. 146 00:09:00,606 --> 00:09:05,177 NARRATOR: Gingerich tried to return to Pakistan to resume his search 147 00:09:05,177 --> 00:09:08,180 but war had broken out, and the borders were closed. 148 00:09:09,682 --> 00:09:13,686 Frustrated, Gingerich decided to look elsewhere. 149 00:09:14,186 --> 00:09:18,691 He had heard stories about whale skeleton sightings 150 00:09:18,691 --> 00:09:20,693 in a very unlikely place. 151 00:09:21,193 --> 00:09:23,696 So he decided to check it out for himself. 152 00:09:26,699 --> 00:09:30,202 The Sahara Desert is one of the driest places on Earth. 153 00:09:32,204 --> 00:09:38,210 But 40 million years ago, things here were quite different. 154 00:09:38,210 --> 00:09:41,714 GINGERICH: This used to be the sea. 155 00:09:41,714 --> 00:09:43,716 Just think of this being 156 00:09:43,716 --> 00:09:47,219 the current Mediterranean coast of Egypt 157 00:09:47,219 --> 00:09:50,222 backed up about 40 million years 158 00:09:50,222 --> 00:09:54,226 but about 100 kilometers to the south of where it is today. 159 00:09:56,729 --> 00:10:00,232 NARRATOR: Here, in what had once been the Southern Mediterranean Sea 160 00:10:00,733 --> 00:10:05,237 is a 100-square-mile stretch of layered sandstone 161 00:10:05,237 --> 00:10:07,740 with a surprising name... 162 00:10:10,242 --> 00:10:12,244 Valley of the Whales. 163 00:10:15,748 --> 00:10:17,750 The name is well suited. 164 00:10:19,752 --> 00:10:23,255 Scattered everywhere across this arid landscape 165 00:10:23,255 --> 00:10:27,259 are what look like heaps of rose-colored stones. 166 00:10:27,259 --> 00:10:29,261 Here's aBasilosaurus. 167 00:10:29,261 --> 00:10:31,764 NARRATOR: But they're not stones... 168 00:10:31,764 --> 00:10:34,767 You can see how big the vertebrae are. 169 00:10:34,767 --> 00:10:37,770 Here's a lumbar partly weathered away. 170 00:10:37,770 --> 00:10:43,275 NARRATOR: They're whale skeletons 40 million years old. 171 00:10:43,776 --> 00:10:46,779 There's another one back here coming out of the mushroom. 172 00:10:46,779 --> 00:10:48,280 There's one over here. 173 00:10:51,283 --> 00:10:53,285 And back over there is one. 174 00:10:56,288 --> 00:10:59,291 This whole place is full of whales. 175 00:11:01,293 --> 00:11:04,797 NARRATOR: Why were there so many whales concentrated in this one spot? 176 00:11:07,299 --> 00:11:09,301 Gingerich believes that Whale Valley 177 00:11:09,301 --> 00:11:11,303 was once a protected bay, 178 00:11:11,303 --> 00:11:16,308 a lagoon hidden from the open sea by underwater sandbars. 179 00:11:19,311 --> 00:11:22,815 Perhaps the whales birthed their young here 180 00:11:22,815 --> 00:11:24,817 and came here to die. 181 00:11:28,320 --> 00:11:31,824 But even with hundreds of whale bones at his feet 182 00:11:31,824 --> 00:11:33,826 Gingerich was disappointed. 183 00:11:33,826 --> 00:11:36,328 Nearly all of the skeletons 184 00:11:36,829 --> 00:11:40,332 belonged to a whale called"Basilosaurus--" 185 00:11:40,332 --> 00:11:44,336 a 40-million-year-old creature already known to science. 186 00:11:46,338 --> 00:11:49,842 Basilosauruslived full time in the water. 187 00:11:49,842 --> 00:11:51,343 This isBasilosaurus. 188 00:11:51,343 --> 00:11:53,345 I got all excited... 189 00:11:53,345 --> 00:11:56,348 NARRATOR: If whales had evolved from land mammals 190 00:11:56,348 --> 00:11:58,851 they had done so long beforeBasilosaurus. 191 00:12:00,853 --> 00:12:05,858 So Gingerich didn't think the bones would be of much interest 192 00:12:05,858 --> 00:12:10,362 but he couldn't have been more wrong. 193 00:12:10,362 --> 00:12:13,866 After only a few days of digging 194 00:12:13,866 --> 00:12:17,369 he made his second amazing find. 195 00:12:18,370 --> 00:12:20,873 It turned out thatBasilosaurus 196 00:12:20,873 --> 00:12:24,877 had something modern whales have long since lost. 197 00:12:24,877 --> 00:12:29,381 For the first time, we've got whales that have legs. 198 00:12:29,381 --> 00:12:32,384 NARRATOR: The bones were small but unmistakable. 199 00:12:33,886 --> 00:12:35,888 A pelvis. 200 00:12:38,390 --> 00:12:39,892 A kneecap. 201 00:12:42,394 --> 00:12:43,896 Even toes. 202 00:12:44,897 --> 00:12:48,901 This whale had a complete set of leg bones. 203 00:12:50,903 --> 00:12:53,405 Gingerich brought back as much of the skeleton 204 00:12:53,405 --> 00:12:54,907 as he could carry. 205 00:12:55,908 --> 00:12:57,409 It was dramatic evidence 206 00:12:57,409 --> 00:13:00,913 that whales had once been four-legged animals. 207 00:13:04,917 --> 00:13:06,418 Since Gingerich's finds 208 00:13:06,418 --> 00:13:11,423 he and others have filled in more of this fantastic story. 209 00:13:13,425 --> 00:13:14,927 Scientists now think 210 00:13:14,927 --> 00:13:18,430 that the earliest ancestor of whales was similar 211 00:13:18,430 --> 00:13:22,935 to this 50 million-year-old wolflike mammal called sinonyx. 212 00:13:25,437 --> 00:13:27,439 Sinonyx was a predatory scavenger 213 00:13:27,439 --> 00:13:31,944 that lived and hunted along the shores of an ancient sea. 214 00:13:31,944 --> 00:13:35,447 Perhaps its descendants found the water 215 00:13:35,447 --> 00:13:40,452 a source of abundant food, and a haven from competition. 216 00:13:40,452 --> 00:13:43,956 Over millions of years front legs became fins 217 00:13:44,456 --> 00:13:47,459 rear legs disappeared, bodies lost fur 218 00:13:47,459 --> 00:13:51,463 and took on their familiar streamlined shape. 219 00:13:54,466 --> 00:13:57,970 Since Gingerich's first find, named Pakicetus 220 00:13:57,970 --> 00:14:01,974 the list of known transitional whales has grown. 221 00:14:01,974 --> 00:14:07,980 It now includes Ambulocetus... 222 00:14:07,980 --> 00:14:10,983 Rhodocetus... 223 00:14:10,983 --> 00:14:14,987 Durodon... 224 00:14:14,987 --> 00:14:17,990 as well as Basilosaurus. 225 00:14:19,992 --> 00:14:22,494 They reveal another element of whale evolution 226 00:14:22,494 --> 00:14:25,497 the gradual migration of nostrils to the top of the head 227 00:14:25,497 --> 00:14:28,000 as whales adapted to breathing in the water. 228 00:14:28,000 --> 00:14:29,001 (exhaling) 229 00:14:29,001 --> 00:14:32,004 GINGERICH: How did whales lose their legs? 230 00:14:32,004 --> 00:14:38,510 As the years went by, they evolved into newer types of... 231 00:14:38,510 --> 00:14:42,514 NARRATOR: Gingerich's work demonstrates what Darwin himself insisted 232 00:14:43,015 --> 00:14:47,019 that the evidence for evolution is all around us 233 00:14:47,019 --> 00:14:50,022 if we choose to look for it. 234 00:14:52,524 --> 00:14:57,529 And bones aren't the only evidence of whale evolution. 235 00:14:57,529 --> 00:15:02,534 Their ancestry is also visible in the way they move. 236 00:15:05,037 --> 00:15:09,541 Frank Fish studies how today's marine mammals swim. 237 00:15:11,543 --> 00:15:15,047 He looks for their evolutionary heritage 238 00:15:15,047 --> 00:15:18,050 in the way they move through the water. 239 00:15:18,050 --> 00:15:20,052 FISH: The big question is: 240 00:15:20,052 --> 00:15:22,554 How do you go from a terrestrial mammal 241 00:15:22,554 --> 00:15:25,057 that ran around on all four legs 242 00:15:25,057 --> 00:15:27,059 to something such as a dolphin 243 00:15:27,059 --> 00:15:29,561 which now doesn't have any legs at all 244 00:15:29,561 --> 00:15:32,064 and is well adapted to swimming in the oceans? 245 00:15:34,066 --> 00:15:40,072 NARRATOR: Even though whales look like fish, they don't swim like them. 246 00:15:40,072 --> 00:15:44,076 Fish swim by flexing their spines from side to side 247 00:15:44,076 --> 00:15:46,578 like this shark. 248 00:15:46,578 --> 00:15:49,581 But mammals swim differently. 249 00:15:52,084 --> 00:15:57,589 This otter swims by undulating its spine up and down... 250 00:15:57,589 --> 00:16:00,592 in exactly the same way that whales do. 251 00:16:02,094 --> 00:16:04,596 And, as it turns out in the same way 252 00:16:04,596 --> 00:16:08,600 that land mammals use their spines when running. 253 00:16:11,603 --> 00:16:14,606 Whales took with them into the water 254 00:16:14,606 --> 00:16:17,109 their ancestral way of moving 255 00:16:17,109 --> 00:16:21,113 and we can still see it... 50 million years later. 256 00:16:25,117 --> 00:16:29,621 SHUBIN: In one sense, evolution didn't invent anything new with whales; 257 00:16:29,621 --> 00:16:32,124 it was just tinkering with land mammals. 258 00:16:32,124 --> 00:16:34,126 It's using the old to make the new 259 00:16:34,126 --> 00:16:36,128 and we call that tinkering. 260 00:16:36,128 --> 00:16:38,130 And it does this in every animal group 261 00:16:38,130 --> 00:16:41,133 at every time during evolutionary history. 262 00:16:43,135 --> 00:16:47,139 NARRATOR: The starting point for whales was a four-legged land animal 263 00:16:47,139 --> 00:16:50,142 that lived over 50 million years ago. 264 00:16:50,142 --> 00:16:54,646 But land animals were also the product of a transformation, 265 00:16:54,646 --> 00:16:57,649 a much earlier one. 266 00:16:59,151 --> 00:17:01,153 Hundreds of millions of years ago 267 00:17:01,153 --> 00:17:03,155 there were no animals on land. 268 00:17:03,155 --> 00:17:06,158 SHUBIN: Before then 269 00:17:06,158 --> 00:17:08,660 all our distant ancestors lived in the water. 270 00:17:08,660 --> 00:17:13,165 So at some point you had this shift from life in water 271 00:17:13,165 --> 00:17:14,666 to life on land. 272 00:17:14,666 --> 00:17:16,668 That's a huge change. 273 00:17:16,668 --> 00:17:20,172 NARRATOR: It was the moment when fish crawled out of the water 274 00:17:20,172 --> 00:17:21,673 and onto land. 275 00:17:21,673 --> 00:17:25,177 WOMAN: If these early animals hadn't made the transition 276 00:17:25,177 --> 00:17:26,678 we wouldn't be here today. 277 00:17:27,179 --> 00:17:30,682 And it's important to understand how and when 278 00:17:30,682 --> 00:17:34,186 and possibly, where that transition took place. 279 00:17:34,186 --> 00:17:40,192 NARRATOR: The first creatures to leave the water really started something. 280 00:17:40,192 --> 00:17:44,696 Their descendants eventually evolved into today's reptiles... 281 00:17:44,696 --> 00:17:47,199 birds... 282 00:17:47,199 --> 00:17:48,700 and mammals. 283 00:17:50,202 --> 00:17:52,704 And these creatures' common origins 284 00:17:52,704 --> 00:17:55,707 are still visible in their bodies. 285 00:17:58,210 --> 00:18:03,215 Just like us, they all have bodies with four limbs, 286 00:18:03,215 --> 00:18:06,218 they're all tetrapods. 287 00:18:06,218 --> 00:18:10,722 SHUBIN: What that means is that all these different creatures 288 00:18:10,722 --> 00:18:13,459 are descended from a common ancestor 289 00:18:13,459 --> 00:18:17,463 whichhadsomething very similar or akin to limbs. 290 00:18:19,465 --> 00:18:22,968 NARRATOR: Just what was that common ancestor? 291 00:18:22,968 --> 00:18:26,972 And how did it leave the water 370 million years ago? 292 00:18:26,972 --> 00:18:29,475 (men conversing) 293 00:18:29,475 --> 00:18:32,978 Those are the questions that paleontologists Neil Shubin 294 00:18:32,978 --> 00:18:35,981 and Ted Daeschler are trying to answer. 295 00:18:35,981 --> 00:18:40,486 They think that the cliffs here in Central Pennsylvania 296 00:18:40,486 --> 00:18:42,488 may offer some clues. 297 00:18:46,992 --> 00:18:49,495 DAESCHLER: All right, I think it's a good day for fossils. 298 00:18:49,995 --> 00:18:50,996 What do you say? 299 00:18:50,996 --> 00:18:52,498 Great day; let's find some. 300 00:18:52,498 --> 00:18:53,499 Hey, Doug. 301 00:18:53,499 --> 00:18:54,500 Hey, Doug. 302 00:18:54,500 --> 00:18:55,501 Good trip up? 303 00:18:55,501 --> 00:18:57,002 What you say we go over here? 304 00:18:57,002 --> 00:18:59,004 That's good. 305 00:18:59,004 --> 00:19:00,506 Get some good digging in today. 306 00:19:00,506 --> 00:19:03,509 NARRATOR: An unlikely spot to hunt for early tetrapod fossils. 307 00:19:03,509 --> 00:19:07,012 But they're here because the rocks in these hills 308 00:19:07,513 --> 00:19:08,514 are just the right age, 309 00:19:08,514 --> 00:19:11,517 laid down during the period in Earth's history 310 00:19:11,517 --> 00:19:13,018 called the Devonian. 311 00:19:13,018 --> 00:19:15,020 (men conversing) 312 00:19:15,020 --> 00:19:18,524 SHUBIN: Back in the Devonian, this place was very different. 313 00:19:18,524 --> 00:19:20,025 It was south of the Equator, 314 00:19:20,025 --> 00:19:23,028 remember the continents are continually moving around, 315 00:19:23,028 --> 00:19:25,030 and back this time we're actually dealing with 316 00:19:25,030 --> 00:19:27,533 a much more tropical climate in Pennsylvania. 317 00:19:27,533 --> 00:19:30,035 NARRATOR: Hundreds of millions of years ago 318 00:19:30,035 --> 00:19:32,538 the fossils and sediments in these layers 319 00:19:32,538 --> 00:19:35,541 were collecting on the bottom of a stream. 320 00:19:40,045 --> 00:19:41,547 SHUBIN: What we have here 321 00:19:41,547 --> 00:19:43,549 is a snapshot of life in a stream 322 00:19:44,049 --> 00:19:46,051 about 370 million years ago. 323 00:19:46,051 --> 00:19:53,058 These are fossilized... broken fossils of scales, of teeth. 324 00:19:53,058 --> 00:19:54,560 This little bone here, 325 00:19:54,560 --> 00:19:58,063 it's a spine of a creature known as a spiny shark. 326 00:19:58,063 --> 00:20:03,569 NARRATOR: Most of the fossils are too fragmented to be of much value. 327 00:20:03,569 --> 00:20:06,071 But in 1995, right at this spot 328 00:20:06,071 --> 00:20:10,576 Daeschler came across something he had never seen before. 329 00:20:13,078 --> 00:20:17,082 It was a small shoulder bone, but not from a fish. 330 00:20:19,585 --> 00:20:24,590 It was a tetrapod shoulder, 370 million years old. 331 00:20:30,095 --> 00:20:33,098 Shubin and Daeschler had unearthed the remains 332 00:20:33,098 --> 00:20:37,102 of one of life's first four-legged creatures. 333 00:20:37,102 --> 00:20:40,606 DAESCHLER: It was the first evidence of these early tetrapods 334 00:20:40,606 --> 00:20:44,610 from all of North America, and that made it very exciting. 335 00:20:48,113 --> 00:20:50,616 NARRATOR: And there was another surprise. 336 00:20:50,616 --> 00:20:52,618 Since it was found in the stream bed 337 00:20:52,618 --> 00:20:55,621 this tetrapod most likely livedin the water. 338 00:20:55,621 --> 00:20:57,623 SHUBIN: And it's a very surprising discovery. 339 00:20:57,623 --> 00:20:58,624 It's not something 340 00:20:59,124 --> 00:21:00,626 we necessarily would have predicted. 341 00:21:00,626 --> 00:21:05,130 NARRATOR: Why would an animal with limbs live in the water? 342 00:21:05,130 --> 00:21:07,633 Limbs were thought to have evolved 343 00:21:07,633 --> 00:21:09,635 for getting around on land. 344 00:21:09,635 --> 00:21:13,138 The old idea was that the fish came on shore first 345 00:21:13,138 --> 00:21:15,140 and then developed the legs. 346 00:21:15,140 --> 00:21:17,142 And what we now think 347 00:21:17,142 --> 00:21:20,646 is that the tetrapods developed the fingers first 348 00:21:20,646 --> 00:21:22,648 and then left the water. 349 00:21:22,648 --> 00:21:25,651 NARRATOR: Jenny Clack of Cambridge University 350 00:21:25,651 --> 00:21:30,656 suspected that the theory taught in many textbooks was wrong. 351 00:21:30,656 --> 00:21:34,159 The story that you will find in many of the old textbooks 352 00:21:34,159 --> 00:21:36,161 and the pictures that you will see 353 00:21:36,161 --> 00:21:38,664 in children's books and museum galleries 354 00:21:38,664 --> 00:21:43,669 is a picture of a fish stranded in a drying pool 355 00:21:43,669 --> 00:21:46,672 trying to support itself out of water. 356 00:21:46,672 --> 00:21:50,676 And it looks really odd if you look at it objectively. 357 00:21:50,676 --> 00:21:54,680 NARRATOR: Clack thought there had to be a better explanation 358 00:21:54,680 --> 00:21:56,682 but where to look? 359 00:21:56,682 --> 00:22:01,186 Only a handful of early tetrapod fossils had ever been found, 360 00:22:01,186 --> 00:22:04,189 most of those in a remote part of Greenland 361 00:22:04,189 --> 00:22:05,691 at the turn of the century. 362 00:22:07,192 --> 00:22:12,197 All she had to guide her was a note scribbled in a journal 363 00:22:12,197 --> 00:22:16,201 from a scouting trip to Greenland years earlier. 364 00:22:16,201 --> 00:22:20,706 It referred to tetrapod fossils on an unnamed mountain. 365 00:22:23,208 --> 00:22:28,213 Clack flew to Greenland to search for those bones. 366 00:22:28,213 --> 00:22:33,218 CLACK: Eventually we found the spot, 800 meters up on a hillside. 367 00:22:33,218 --> 00:22:36,722 NARRATOR: Clack returned with four tons of rock... 368 00:22:38,223 --> 00:22:42,227 And spent the next four years drilling. 369 00:22:44,730 --> 00:22:46,732 At the end 370 00:22:46,732 --> 00:22:50,235 she had the most complete early tetrapod skeleton ever found; 371 00:22:50,235 --> 00:22:53,238 and it forever changed the textbooks. 372 00:22:53,238 --> 00:22:55,741 CLACK: One of the first things 373 00:22:55,741 --> 00:23:00,245 that we found was this forelimb. 374 00:23:00,245 --> 00:23:04,249 NARRATOR: At the end of the animal's limb 375 00:23:04,249 --> 00:23:07,753 was an unmistakable array of bones. 376 00:23:07,753 --> 00:23:10,756 This was a hand. 377 00:23:10,756 --> 00:23:12,257 CLACK: This is a life reconstruction.. 378 00:23:12,257 --> 00:23:15,260 The artist is using imagination on the color scheme 379 00:23:15,260 --> 00:23:17,262 and on the eyes 380 00:23:17,262 --> 00:23:20,265 but we think this is as accurate as you can get. 381 00:23:20,265 --> 00:23:23,769 NARRATOR: The creature, named Acanthostega 382 00:23:23,769 --> 00:23:26,271 was clearly a water-dweller: 383 00:23:26,271 --> 00:23:33,779 It had a fishlike tail and gills for breathing in the water. 384 00:23:34,279 --> 00:23:37,783 But the ends of its arms were petal-shaped... 385 00:23:37,783 --> 00:23:41,286 possibly the first hands on Earth. 386 00:23:41,286 --> 00:23:45,791 CLACK: This was a swimming creature. 387 00:23:45,791 --> 00:23:47,793 We don't know whether it could ever have come out on land 388 00:23:48,293 --> 00:23:50,295 but it certainly wouldn't havewalked 389 00:23:50,295 --> 00:23:51,797 in the conventional sense. 390 00:23:51,797 --> 00:23:55,801 Basically, it's... a fish with fingers. 391 00:23:55,801 --> 00:24:01,306 NARRATOR: Clack's find was a scientific breakthrough. 392 00:24:01,306 --> 00:24:06,812 It proved that some fish had arms and legs in the water. 393 00:24:08,814 --> 00:24:13,819 So tetrapods didn't need to grow limbs after they got onto land. 394 00:24:16,321 --> 00:24:20,826 The limbs had already evolved 395 00:24:20,826 --> 00:24:23,328 and helped them survive out of the water. 396 00:24:23,328 --> 00:24:26,331 The basic pattern for limbs had been in place 397 00:24:26,331 --> 00:24:28,834 for millions of years. 398 00:24:28,834 --> 00:24:31,336 SHUBIN: Here we have the fin 399 00:24:31,336 --> 00:24:36,341 of a 370-million-year-old fossil fish and an arm of a human. 400 00:24:36,341 --> 00:24:40,345 In a human arm, what you have is one bone... 401 00:24:40,345 --> 00:24:45,851 then two bones, the wrist and the digits. 402 00:24:45,851 --> 00:24:47,853 In this fin what do you have? 403 00:24:47,853 --> 00:24:50,355 You have one bone, two bones... 404 00:24:52,858 --> 00:24:57,362 even little bones that can be compared to a wrist 405 00:24:57,362 --> 00:24:58,864 and then rods that face away 406 00:24:58,864 --> 00:25:01,366 from the rest of the appendage itself 407 00:25:01,366 --> 00:25:03,869 just like our fingers or toes. 408 00:25:03,869 --> 00:25:05,871 So you have, in a fish fin 409 00:25:05,871 --> 00:25:09,374 already set up about 370 million years ago 410 00:25:09,374 --> 00:25:13,378 many of the bones that are used in a tetrapod limb. 411 00:25:13,378 --> 00:25:16,882 NARRATOR: With the basic pattern already there 412 00:25:16,882 --> 00:25:19,384 the fin-to-limb transition took place 413 00:25:19,384 --> 00:25:21,887 in a series of small changes 414 00:25:21,887 --> 00:25:24,389 occurring over millions of years. 415 00:25:24,389 --> 00:25:26,391 SHUBIN: There's really no goal to evolution. 416 00:25:26,391 --> 00:25:28,894 Evolution wasn'ttrying to make limbs 417 00:25:28,894 --> 00:25:31,396 it wasn'ttrying to push our distant ancestors 418 00:25:31,396 --> 00:25:33,398 out of the water. 419 00:25:33,398 --> 00:25:36,401 What was happening was a series of experiments. 420 00:25:37,903 --> 00:25:40,405 NARRATOR: In the crowded, freshwater streams 421 00:25:40,405 --> 00:25:41,907 where tetrapods first evolved 422 00:25:41,907 --> 00:25:46,411 the competition for survival was intense. 423 00:25:46,411 --> 00:25:49,414 SHUBIN: These small streams were like an engine 424 00:25:49,414 --> 00:25:51,416 or a crucible of evolutionary change. 425 00:25:52,918 --> 00:25:56,922 NARRATOR: Fish experimented with all sorts of survival strategies. 426 00:25:59,424 --> 00:26:01,426 Some became predators. 427 00:26:01,426 --> 00:26:05,430 The owner of this jaw was a 12-foot-long killer. 428 00:26:07,432 --> 00:26:10,435 Its teeth were the size of railroad spikes. 429 00:26:12,437 --> 00:26:16,942 Smaller fish developed elaborate defenses, like this heavy armor. 430 00:26:20,445 --> 00:26:24,449 Others packed weaponry, like this sharp spike. 431 00:26:24,449 --> 00:26:27,452 It protruded from behind its owner's neck. 432 00:26:30,956 --> 00:26:34,459 These armaments were all tools for survival 433 00:26:34,459 --> 00:26:37,462 in a dangerous world. 434 00:26:37,462 --> 00:26:41,466 Perhaps their new arms and legs gave the first tetrapods 435 00:26:41,466 --> 00:26:43,969 another way to survive. 436 00:26:43,969 --> 00:26:46,972 SHUBIN: It was to get out of the way; it was to get onto land. 437 00:26:46,972 --> 00:26:48,974 And what enabled those animals 438 00:26:48,974 --> 00:26:51,977 to get out of the way, that is, to get out of the water 439 00:26:51,977 --> 00:26:53,478 were these new features, like limbs. 440 00:26:55,981 --> 00:26:59,985 NARRATOR: Those that did escape found a new world 441 00:26:59,985 --> 00:27:02,487 filled with opportunity. 442 00:27:08,994 --> 00:27:11,363 The transformation from water to land 443 00:27:11,363 --> 00:27:13,365 was only the latest example 444 00:27:13,365 --> 00:27:16,868 of evolution experimenting with radically new forms. 445 00:27:20,372 --> 00:27:22,374 An earlier transformation, 446 00:27:22,374 --> 00:27:24,876 perhaps the most significant of all, 447 00:27:24,876 --> 00:27:28,380 occurred just over half a billion years ago... 448 00:27:30,882 --> 00:27:34,386 And it led to all animals as we know them. 449 00:27:37,389 --> 00:27:40,392 Evolution tinkered with fish to make limbs. 450 00:27:40,392 --> 00:27:42,894 But fish carry the baggage of their own past. 451 00:27:42,894 --> 00:27:45,897 Think of a fish: 452 00:27:45,897 --> 00:27:50,402 It has a head, it has a tail and a bunch of fins in between. 453 00:27:50,402 --> 00:27:53,905 That's a body plan, the way the body's put together. 454 00:27:53,905 --> 00:27:57,409 But that's just one of many ways of putting animals together. 455 00:27:57,409 --> 00:28:00,912 I mean, some animals are like disks, like jellyfish. 456 00:28:00,912 --> 00:28:03,915 Other animals have lots of little legs. 457 00:28:03,915 --> 00:28:05,417 The question is 458 00:28:05,417 --> 00:28:09,421 what sort of tinkering led to these body plans? 459 00:28:10,922 --> 00:28:12,924 I mean, really what we're dealing with here 460 00:28:12,924 --> 00:28:14,426 is the origin of animals. 461 00:28:15,927 --> 00:28:17,929 NARRATOR: According to the fossil record 462 00:28:17,929 --> 00:28:20,932 animals appeared upon the earth in a short burst 463 00:28:20,932 --> 00:28:24,436 around 570 million years ago. 464 00:28:26,438 --> 00:28:29,941 Scientists call this crucial transformation 465 00:28:29,941 --> 00:28:32,944 the Cambrian Explosion. 466 00:28:32,944 --> 00:28:34,946 MAN: The Cambrian Explosion was effectively 467 00:28:34,946 --> 00:28:36,448 one of the greatest breakthroughs 468 00:28:36,448 --> 00:28:37,949 in the history of life. 469 00:28:39,451 --> 00:28:42,954 About half a billion years ago, suddenly, things change 470 00:28:42,954 --> 00:28:46,958 and we have this extraordinary explosion of diversity. 471 00:28:46,958 --> 00:28:49,961 And this sudden appearance of the fossils led to this term 472 00:28:49,961 --> 00:28:51,463 the Cambrian Explosion. 473 00:28:51,463 --> 00:28:53,965 And Darwin, as ever, was extremely candid. 474 00:28:54,466 --> 00:28:56,968 He said, "Look, this is a problem for my theory. 475 00:28:56,968 --> 00:29:00,472 How is it that suddenly, animals seem to come out of nowhere?" 476 00:29:00,472 --> 00:29:03,975 And to a certain extent, that is still something of a mystery. 477 00:29:03,975 --> 00:29:07,979 NARRATOR: Most of what we know of the Cambrian Explosion 478 00:29:07,979 --> 00:29:10,482 is a result of a single discovery 479 00:29:10,482 --> 00:29:13,485 probably the greatest fossil find in history. 480 00:29:14,986 --> 00:29:18,990 In 1913, while climbing in the Canadian Rockies 481 00:29:18,990 --> 00:29:22,994 paleontologist Charles Walcott discovered a layer of shale 482 00:29:22,994 --> 00:29:27,499 containing thousands of exquisitely detailed fossils. 483 00:29:29,000 --> 00:29:33,004 These animals, all sea dwellers 484 00:29:33,004 --> 00:29:37,008 were caught in a catastrophic underwater mudslide. 485 00:29:39,010 --> 00:29:42,514 Over the next 500 million years 486 00:29:42,514 --> 00:29:45,016 the sea floor which entombed them 487 00:29:45,016 --> 00:29:47,519 rose to become the top of a mountain. 488 00:29:49,020 --> 00:29:53,024 Walcott removed over 60,000 fossils from the site 489 00:29:53,024 --> 00:29:56,528 which he named the Burgess Shale. 490 00:29:58,530 --> 00:30:02,534 Simon Conway Morris has studied the fossils for over 30 years. 491 00:30:04,536 --> 00:30:06,538 It's almost as if you've gone to another planet. 492 00:30:06,538 --> 00:30:08,039 You've been given a fishing boat and a net 493 00:30:08,039 --> 00:30:10,041 and you've been allowed to throw that net 494 00:30:10,041 --> 00:30:11,543 over into the deep ocean 495 00:30:11,543 --> 00:30:13,044 and you'd no idea what was going to come up. 496 00:30:13,044 --> 00:30:17,048 NARRATOR: Some of the Burgess Shale creatures were familiar. 497 00:30:17,048 --> 00:30:19,050 MORRIS: And here, we've got one of the trilobites. 498 00:30:19,050 --> 00:30:22,053 We see the delicate soft parts, also preserved. 499 00:30:22,053 --> 00:30:26,057 NARRATOR: Trilobites are extinct arthropods 500 00:30:26,057 --> 00:30:29,060 creatures with external skeletons. 501 00:30:29,060 --> 00:30:33,064 Today's arthropods, like crabs, lobsters 502 00:30:33,064 --> 00:30:35,066 insects and spiders 503 00:30:35,066 --> 00:30:38,069 are all descendants of creatures like these. 504 00:30:38,069 --> 00:30:43,575 Other Burgess Shale animals were bizarre, alien-seeming. 505 00:30:43,575 --> 00:30:47,579 An animal with five eyes and a long retractable nozzle. 506 00:30:50,081 --> 00:30:53,585 One with long, sharp spines protruding from its back. 507 00:30:56,087 --> 00:30:59,591 Another with a circle of prongs around its mouth. 508 00:31:04,095 --> 00:31:07,098 And yet, as alien as these creatures seem 509 00:31:07,098 --> 00:31:09,601 they are also surprisingly familiar. 510 00:31:13,104 --> 00:31:15,106 Like living animals, they have bodies 511 00:31:15,106 --> 00:31:19,611 with heads, tails, appendages, 512 00:31:19,611 --> 00:31:24,616 specialized segments performing specialized functions. 513 00:31:24,616 --> 00:31:30,121 All the basic body plans found in nature today are here. 514 00:31:31,623 --> 00:31:34,626 Every animal that has lived for the last half billion years 515 00:31:35,126 --> 00:31:38,630 has come from tinkering with these initial designs. 516 00:31:42,634 --> 00:31:45,637 We might even see our own ancestor here. 517 00:31:45,637 --> 00:31:49,641 MORRIS: Maybe this is the crown of the Burgess Shale. 518 00:31:49,641 --> 00:31:51,643 This isPikaia. 519 00:31:51,643 --> 00:31:55,647 NARRATOR: A tiny creature,Pikaiais one of the rarest fossils 520 00:31:55,647 --> 00:31:57,148 from the Burgess Shale. 521 00:31:57,148 --> 00:32:00,652 It's the only one with an internal nerve cord 522 00:32:00,652 --> 00:32:03,655 resembling a spine. 523 00:32:03,655 --> 00:32:06,157 That might mean that creatures likePikaia 524 00:32:06,157 --> 00:32:10,662 were the earliest ancestors of all animals with skeletons. 525 00:32:10,662 --> 00:32:14,666 MORRIS: The idea is that this might be the precursor of the fish 526 00:32:14,666 --> 00:32:16,668 and so, ultimately 527 00:32:16,668 --> 00:32:19,671 through a long evolutionary story, ourselves. 528 00:32:19,671 --> 00:32:22,173 The Cambrian Explosion matters for lots of reasons. 529 00:32:22,173 --> 00:32:23,675 Basically, it's part of our history. 530 00:32:23,675 --> 00:32:26,678 It's where we came from and that matters very much. 531 00:32:26,678 --> 00:32:29,681 This is the time when the animals first appear. 532 00:32:29,681 --> 00:32:33,685 We look back and we can see part of our history unfolding. 533 00:32:37,689 --> 00:32:39,691 So what do we learn by looking 534 00:32:39,691 --> 00:32:42,193 at 600 million years of animal history? 535 00:32:42,694 --> 00:32:47,198 Evolution's tinkering with mammalness to make whales. 536 00:32:47,198 --> 00:32:49,200 In the same way, it's tinkering with fishiness 537 00:32:49,200 --> 00:32:52,203 to make tetrapods 538 00:32:52,203 --> 00:32:54,205 and it's tinkering with animalness 539 00:32:54,205 --> 00:32:57,208 to make all the different body plans that we see. 540 00:32:57,208 --> 00:33:03,214 All these different creatures are variations of the same theme 541 00:33:03,214 --> 00:33:06,718 restated over and over again. 542 00:33:06,718 --> 00:33:11,723 The question was, what was evolution tinkering with? 543 00:33:11,723 --> 00:33:13,725 One of the remarkable discoveries 544 00:33:13,725 --> 00:33:15,226 of the last 20 years 545 00:33:15,226 --> 00:33:19,731 is that evolution's not tinkering with the bodies. 546 00:33:19,731 --> 00:33:21,733 It's tinkering with the recipe 547 00:33:21,733 --> 00:33:24,235 the machinery that builds bodies. 548 00:33:24,235 --> 00:33:26,237 What is that recipe? 549 00:33:26,237 --> 00:33:27,238 What is that machinery? 550 00:33:27,238 --> 00:33:28,239 It's the genes. 551 00:33:31,242 --> 00:33:35,747 NARRATOR: Fossils record the changes in animals' bodies over time 552 00:33:35,747 --> 00:33:39,751 but just how bodies change was unknown. 553 00:33:41,753 --> 00:33:44,756 The search for the genetic mechanism of evolution 554 00:33:44,756 --> 00:33:47,759 took most of this century. 555 00:33:47,759 --> 00:33:51,262 When scientists finally found it 556 00:33:51,262 --> 00:33:53,264 they were astonished... 557 00:33:54,265 --> 00:33:57,268 by just how simple it was. 558 00:34:00,271 --> 00:34:03,775 One of the key players was Mike Levine. 559 00:34:03,775 --> 00:34:07,278 LEVINE: I was, um, I guess, kind of a weird kid. 560 00:34:07,278 --> 00:34:08,780 I always liked bugs. 561 00:34:08,780 --> 00:34:11,783 We had a nice, big backyard, and I could go back there. 562 00:34:11,783 --> 00:34:13,284 It was kind of a sanctuary. 563 00:34:13,284 --> 00:34:16,287 And, uh, I played with bugs... 564 00:34:16,287 --> 00:34:18,790 dissected them, manipulated them. 565 00:34:18,790 --> 00:34:20,792 That's really the most pleasant memory I have. 566 00:34:20,792 --> 00:34:26,297 NARRATOR: Levine's affinity for bugs led to his study of biology. 567 00:34:26,297 --> 00:34:31,302 One insect in particular became an object of fascination. 568 00:34:31,302 --> 00:34:34,806 LEVINE: They have a quick generation time 569 00:34:34,806 --> 00:34:36,808 and they have lots of pattern. 570 00:34:37,308 --> 00:34:39,310 I mean, you wouldn't know it if you look at a distance 571 00:34:39,310 --> 00:34:40,812 but when you look under a microscope 572 00:34:41,312 --> 00:34:42,814 at an adult fruit fly 573 00:34:42,814 --> 00:34:46,818 you'd be astounded by the number of bristles 574 00:34:46,818 --> 00:34:51,322 the intricacies of their wings, the patterns of their eyes. 575 00:34:52,323 --> 00:34:54,826 But the embryos are something else. 576 00:34:54,826 --> 00:34:56,327 I do love the embryos. 577 00:34:56,327 --> 00:34:58,329 NARRATOR: Scientists had long suspected 578 00:34:58,329 --> 00:35:03,334 that embryos held clues to how animals evolve. 579 00:35:06,838 --> 00:35:09,340 All embryos start out as clusters 580 00:35:09,340 --> 00:35:11,342 of nearly identical cells. 581 00:35:14,846 --> 00:35:17,849 But soon, an embryo partitions itself 582 00:35:17,849 --> 00:35:20,852 into specialized segments 583 00:35:20,852 --> 00:35:25,356 which develop into the final form of the animal. 584 00:35:26,357 --> 00:35:29,360 What controlled this process? 585 00:35:29,360 --> 00:35:32,864 How did the embryos know what shape to take? 586 00:35:34,866 --> 00:35:37,368 One of the first people to study these questions 587 00:35:37,368 --> 00:35:40,872 was a 19th-century naturalist named William Bateson. 588 00:35:43,875 --> 00:35:46,377 Bateson wrote that animals' skeletons revealed 589 00:35:46,377 --> 00:35:50,882 an underlying structure of repeating segments. 590 00:35:58,890 --> 00:36:02,393 He also observed that animals occasionally developed 591 00:36:02,393 --> 00:36:05,396 with some segments in the wrong places. 592 00:36:06,898 --> 00:36:09,901 MAN: Insects with legs in the wrong place. 593 00:36:09,901 --> 00:36:13,404 Crabs where a claw was transformed into a leg. 594 00:36:13,404 --> 00:36:14,805 Pythons with extra ribs 595 00:36:14,805 --> 00:36:16,807 or frogs with extra cervical vertebrae 596 00:36:16,807 --> 00:36:18,309 and all these sorts of things. 597 00:36:19,810 --> 00:36:23,314 NARRATOR: To Bateson, these developmental errors meant 598 00:36:23,314 --> 00:36:25,816 that the underlying blueprint for the animal 599 00:36:25,816 --> 00:36:28,819 was being disrupted. 600 00:36:28,819 --> 00:36:31,322 He had no idea how it happened 601 00:36:31,322 --> 00:36:33,824 but he suspected that these random changes 602 00:36:33,824 --> 00:36:37,828 might provide the fuel for evolution. 603 00:36:40,831 --> 00:36:44,335 By the 1940s, scientists working with fruit flies 604 00:36:44,335 --> 00:36:46,837 had learned how to cause disruptions 605 00:36:46,837 --> 00:36:50,341 in the developmental blueprint: 606 00:36:50,341 --> 00:36:55,846 by dousing growing embryos with radiation and poison. 607 00:36:55,846 --> 00:36:57,348 MAN: And so when they did that 608 00:36:57,348 --> 00:37:01,352 they found flies with changed wing structures, changed legs 609 00:37:01,352 --> 00:37:03,354 and these very special flies 610 00:37:03,354 --> 00:37:06,857 that have one part of the body in the wrong place 611 00:37:06,857 --> 00:37:09,860 or a copy of a normal part of the body in another place. 612 00:37:16,867 --> 00:37:18,869 NARRATOR: The scientists had triggered the changes 613 00:37:19,370 --> 00:37:22,873 by damaging the flies' DNA. 614 00:37:24,875 --> 00:37:26,877 Within each cell of the developing embryo 615 00:37:26,877 --> 00:37:31,382 is a chainlike molecule called DNA. 616 00:37:31,382 --> 00:37:34,385 The experiments showed that DNA was somehow 617 00:37:34,385 --> 00:37:37,388 causing the embryo to divide into segments. 618 00:37:40,391 --> 00:37:42,893 But how? 619 00:37:42,893 --> 00:37:45,396 Scientists were just beginning to grasp 620 00:37:45,396 --> 00:37:51,402 that the DNA itself was made up of segments, called genes. 621 00:37:52,903 --> 00:37:56,907 The question was: how did the genes shape the body? 622 00:38:00,911 --> 00:38:03,914 One researcher, Dr. Ed Lewis of Caltech 623 00:38:03,914 --> 00:38:07,418 studied this question for 30 years 624 00:38:07,418 --> 00:38:10,921 by crossbreeding thousands of flies. 625 00:38:12,423 --> 00:38:15,926 Lewis's work led him to a controversial idea. 626 00:38:15,926 --> 00:38:19,430 He proposed that a surprisingly simple mechanism 627 00:38:19,430 --> 00:38:23,434 was shaping embryos. 628 00:38:23,434 --> 00:38:25,936 He wrote that each segment of the fly 629 00:38:25,936 --> 00:38:29,940 was being directed to grow by a single gene. 630 00:38:29,940 --> 00:38:33,944 A small set of genes, a kind of genetic toolkit 631 00:38:33,944 --> 00:38:36,947 appeared to be laying out the entire body. 632 00:38:38,449 --> 00:38:39,950 And as he looked at these genes, he said 633 00:38:39,950 --> 00:38:41,952 "This one affects this part of the body. 634 00:38:41,952 --> 00:38:43,454 "This affects the next part of the body. 635 00:38:43,454 --> 00:38:45,456 And this affects the next part of the body." 636 00:38:45,456 --> 00:38:47,958 That was an astonishing observation. 637 00:38:49,960 --> 00:38:53,464 NARRATOR: It was astonishing because it seemed too simple. 638 00:38:53,464 --> 00:38:55,966 Nobody else thought single genes were powerful enough 639 00:38:55,966 --> 00:39:00,471 to control something as complex as the structure of the body. 640 00:39:02,473 --> 00:39:06,477 Skeptics argued that Lewis's idea was guesswork. 641 00:39:06,477 --> 00:39:09,980 Of course, he had never seen the genes 642 00:39:09,980 --> 00:39:12,983 because the techniques to do so didn't exist. 643 00:39:14,985 --> 00:39:16,487 From the 1920s to the 1970s 644 00:39:16,487 --> 00:39:19,490 it was not possible to physically isolate 645 00:39:19,490 --> 00:39:20,991 any specific gene. 646 00:39:20,991 --> 00:39:24,495 That opportunity first became available, fortunately for me 647 00:39:24,495 --> 00:39:26,497 at the time that I was a student. 648 00:39:26,497 --> 00:39:29,500 And so, many of us thought, "Wow. 649 00:39:29,500 --> 00:39:32,503 "We can finally dig in there 650 00:39:32,503 --> 00:39:35,506 and identify these really mysterious genes." 651 00:39:38,008 --> 00:39:41,512 NARRATOR: Levine enlisted his friend and fellow scientist Bill McGinnis. 652 00:39:43,514 --> 00:39:46,517 The first gene they went after had an unusual name. 653 00:39:48,519 --> 00:39:52,523 Antennapedia, which means "antenna leg." 654 00:39:55,025 --> 00:39:58,529 The gene was thought to control the growth of legs. 655 00:40:00,531 --> 00:40:02,533 When the gene misfired 656 00:40:02,533 --> 00:40:06,537 flies grew legs in the wrong place: 657 00:40:06,537 --> 00:40:09,540 on their heads, in place of antennae. 658 00:40:11,041 --> 00:40:14,545 In normal flies, legs grow from the midsection 659 00:40:14,545 --> 00:40:17,548 the area called the thorax. 660 00:40:17,548 --> 00:40:22,052 So Levine and McGinnis decided to hunt for the gene 661 00:40:22,052 --> 00:40:24,054 in the thorax of a normal embryo. 662 00:40:26,557 --> 00:40:27,558 LEVINE: The expectation 663 00:40:27,558 --> 00:40:30,561 is that antennapedia would be active 664 00:40:30,561 --> 00:40:32,563 expressed in the thorax 665 00:40:32,563 --> 00:40:34,064 the developing thorax, of the embryo. 666 00:40:34,064 --> 00:40:36,066 But who knew? 667 00:40:36,066 --> 00:40:38,569 NARRATOR: Levine and McGinnis had to do something 668 00:40:38,569 --> 00:40:42,072 no one had ever done before. 669 00:40:42,072 --> 00:40:45,576 They had to find a way to see a gene in action. 670 00:40:47,578 --> 00:40:50,080 LEVINE: We wanted to light up the gene 671 00:40:50,080 --> 00:40:53,083 and it was very painstaking work. 672 00:40:53,083 --> 00:40:57,087 NARRATOR: The project called for new and untested methods. 673 00:40:59,089 --> 00:41:01,091 McGINNIS: At first, it didn't work very well 674 00:41:01,091 --> 00:41:04,595 and there were a number of technical problems to solve. 675 00:41:07,097 --> 00:41:09,600 NARRATOR: The team had to find a delicate balance 676 00:41:10,100 --> 00:41:13,103 of radioactive probes and toxic enzymes. 677 00:41:15,606 --> 00:41:19,610 Too much of either would destroy the embryos. 678 00:41:21,612 --> 00:41:23,614 LEVINE: The process was not very gratifying 679 00:41:23,614 --> 00:41:26,617 on a day-by-day basis. 680 00:41:26,617 --> 00:41:28,619 Unbelievably tedious. 681 00:41:31,622 --> 00:41:34,625 NARRATOR: It took months of trial and error. 682 00:41:40,130 --> 00:41:43,133 McGINNIS: People often said, "You know, you should try something else. 683 00:41:43,133 --> 00:41:47,638 "You know, this is too long-shot. 684 00:41:47,638 --> 00:41:51,141 You know, you're going to... you're just wasting your time." 685 00:41:51,141 --> 00:41:52,142 But we kept going. 686 00:41:56,146 --> 00:42:01,151 NARRATOR: Finally, late one night, all the work paid off. 687 00:42:10,661 --> 00:42:13,163 LEVINE: And there was this moment... 688 00:42:13,163 --> 00:42:17,668 when we saw that the gene was turned on in a band 689 00:42:17,668 --> 00:42:20,671 in the middle of a very early embryo. 690 00:42:20,671 --> 00:42:23,173 This had never been seen before. 691 00:42:23,173 --> 00:42:28,679 NARRATOR: The antennapedia gene was acting like a master switch 692 00:42:28,679 --> 00:42:31,181 turning on the segment of the embryo 693 00:42:31,181 --> 00:42:33,684 that would become the thorax. 694 00:42:33,684 --> 00:42:37,187 The implications were mind-boggling: 695 00:42:37,187 --> 00:42:40,691 if single genes like antennapedia could define 696 00:42:41,191 --> 00:42:43,193 whole segments of an animal 697 00:42:43,193 --> 00:42:47,197 these genes were acting like architects of the body. 698 00:42:49,199 --> 00:42:53,704 And if one of these genes turned on in the wrong place 699 00:42:53,704 --> 00:42:56,707 striking changes to the body could result. 700 00:42:58,208 --> 00:43:01,712 It seemed that Levine and McGinnis had uncovered 701 00:43:01,712 --> 00:43:04,715 the genes responsible for the evolution of bodies. 702 00:43:06,216 --> 00:43:09,219 But there were still doubts. 703 00:43:09,219 --> 00:43:12,723 The work had all been done in fruit flies. 704 00:43:12,723 --> 00:43:14,725 What about other animals? 705 00:43:14,725 --> 00:43:19,229 Did they use the same mechanism to build their bodies? 706 00:43:20,230 --> 00:43:24,234 An answer would come from Switzerland. 707 00:43:24,234 --> 00:43:28,238 In 1994, Walter Gehring of the University of Basel 708 00:43:28,238 --> 00:43:30,741 isolated the gene that triggered 709 00:43:30,741 --> 00:43:33,243 the growth of eyes in fruit flies. 710 00:43:35,746 --> 00:43:37,748 The gene was called Eyeless 711 00:43:37,748 --> 00:43:41,251 because flies without it developed with no eyes. 712 00:43:44,254 --> 00:43:48,759 Gehring knew of a gene in mice that worked in the same way. 713 00:43:51,261 --> 00:43:54,765 He wondered, were the two genes the same? 714 00:43:54,765 --> 00:43:57,267 GEHRING: And this question we tested 715 00:43:57,267 --> 00:44:02,272 by taking the mouse gene and putting it into fruit flies 716 00:44:02,272 --> 00:44:05,275 to see whether flies can understand 717 00:44:05,275 --> 00:44:07,277 the message of the mouse. 718 00:44:07,277 --> 00:44:12,783 NARRATOR: Gehring replaced a fly's gene for eyes with the mouse gene. 719 00:44:14,284 --> 00:44:17,287 GEHRING: And to everybody's surprise 720 00:44:17,287 --> 00:44:20,290 the mouse gene works perfectly well 721 00:44:20,290 --> 00:44:24,795 and can induce a compound eye in the fruit fly. 722 00:44:27,297 --> 00:44:31,301 NARRATOR: The fruit fly grew normal fruit fly eyes 723 00:44:31,301 --> 00:44:33,804 using a gene from a mouse. 724 00:44:33,804 --> 00:44:38,308 Not only did the two creatures use the same mechanism; 725 00:44:38,308 --> 00:44:40,310 they used the same gene. 726 00:44:42,312 --> 00:44:46,817 This was the mechanism behind extra wings 727 00:44:46,817 --> 00:44:52,823 legs sprouting from heads, and Bateson's deformed animals. 728 00:44:54,825 --> 00:44:58,328 The century-long search was complete. 729 00:44:58,328 --> 00:45:01,832 The genetic engine of the body's evolution 730 00:45:01,832 --> 00:45:05,836 turned out to be a tiny handful of powerful genes. 731 00:45:05,836 --> 00:45:07,337 CARROLL: So what this means is 732 00:45:07,337 --> 00:45:10,174 in some ways, some sense, evolution is a simpler process 733 00:45:10,174 --> 00:45:11,675 than we first thought... 734 00:45:13,177 --> 00:45:17,181 when you think about all of the diversity of forms out there. 735 00:45:17,181 --> 00:45:20,184 We first believed that this would involve 736 00:45:20,184 --> 00:45:22,186 all sorts of novel creations 737 00:45:22,186 --> 00:45:25,189 starting from scratch, again and again and again. 738 00:45:25,189 --> 00:45:28,192 We now understand that no, that evolution works 739 00:45:28,192 --> 00:45:31,195 with packets of information, and uses them 740 00:45:31,195 --> 00:45:35,199 in new and different ways and new and different combinations 741 00:45:35,199 --> 00:45:38,202 without necessarily having to invent 742 00:45:38,202 --> 00:45:42,206 anything fundamentally new, but new combinations. 743 00:45:42,206 --> 00:45:47,211 NARRATOR: Suddenly, the commonality of form among animals 744 00:45:47,211 --> 00:45:48,712 was understood: 745 00:45:48,712 --> 00:45:52,716 animals resembled each other because they all used 746 00:45:52,716 --> 00:45:56,220 the same set of genes to build their bodies 747 00:45:56,220 --> 00:46:00,224 a set of genes inherited from a common ancestor 748 00:46:00,224 --> 00:46:03,227 that lived long ago. 749 00:46:03,227 --> 00:46:07,231 And what we see now among all the animals are just variations 750 00:46:07,231 --> 00:46:10,234 on a body plan that existed half a billion years ago. 751 00:46:10,734 --> 00:46:13,237 And there's only one inescapable conclusion 752 00:46:13,237 --> 00:46:15,739 you can draw from that, which is 753 00:46:15,739 --> 00:46:17,741 if all of these branches have these genes 754 00:46:18,242 --> 00:46:20,244 then you have to go to the base of that 755 00:46:20,244 --> 00:46:23,247 which is the last common ancestor of all animals 756 00:46:23,247 --> 00:46:26,250 and you deduce, itmust have had these genes. 757 00:46:26,250 --> 00:46:28,252 So the whole radiation of animals 758 00:46:28,252 --> 00:46:30,754 the whole spring of animal diversity 759 00:46:30,754 --> 00:46:34,258 has been fed by essentially the same set of genes. 760 00:46:35,759 --> 00:46:39,763 NARRATOR: Ed Lewis shared the Nobel Prize in 1995 761 00:46:39,763 --> 00:46:43,767 for the discovery of the universal set of genes 762 00:46:43,767 --> 00:46:46,770 that builds the bodies of animals. 763 00:46:48,272 --> 00:46:51,275 And so, yes, it came as a huge surprise 764 00:46:51,275 --> 00:46:54,278 not only to people like my mother, who says 765 00:46:54,278 --> 00:46:56,280 "My God, an earthworm and a mouse? 766 00:46:56,280 --> 00:46:59,783 An earthworm and me, you know, share things in common?" 767 00:46:59,783 --> 00:47:03,287 But it came as a surprise to other scientists that there was 768 00:47:03,287 --> 00:47:06,790 this profound conservation of mechanism of building embryos 769 00:47:06,790 --> 00:47:09,293 among all these different kinds of animals. 770 00:47:12,796 --> 00:47:15,299 NARRATOR: What about us? 771 00:47:15,299 --> 00:47:16,800 Our bodies are built 772 00:47:16,800 --> 00:47:21,305 from the same genes that build all other animals. 773 00:47:21,305 --> 00:47:24,808 Yet we are different. 774 00:47:24,808 --> 00:47:32,816 No other animal designs... or creates like we do. 775 00:47:34,318 --> 00:47:37,821 We seem so special it's hard not to think 776 00:47:37,821 --> 00:47:42,326 that we're somehow an exception to evolution... 777 00:47:42,326 --> 00:47:44,828 but of course, we're not. 778 00:47:46,330 --> 00:47:48,332 The transformation that led to us 779 00:47:48,332 --> 00:47:51,835 was no different from other transformations. 780 00:47:54,338 --> 00:47:58,342 Our crucial turning point seems to have occurred 781 00:47:58,342 --> 00:48:00,844 when our ancestors left the trees 782 00:48:00,844 --> 00:48:03,347 and began to walk on two legs. 783 00:48:03,347 --> 00:48:06,850 MAN: We don't know exactly when, or even where 784 00:48:06,850 --> 00:48:09,853 our ancestors became upright and bipedal. 785 00:48:09,853 --> 00:48:13,357 We think it goes back well over four million years. 786 00:48:13,357 --> 00:48:15,859 When these ancestors came out of the trees 787 00:48:15,859 --> 00:48:18,862 and began to exploit food sources on the ground 788 00:48:18,862 --> 00:48:20,364 in terrestrial habitats 789 00:48:20,864 --> 00:48:24,368 one of the key elements that would've been so useful to them 790 00:48:24,368 --> 00:48:27,371 would've been freeing their forelimbs, their hands 791 00:48:27,371 --> 00:48:30,874 to be able to gather and carry foodstuffs over long distances. 792 00:48:30,874 --> 00:48:33,377 Once that happened, it opened up 793 00:48:33,377 --> 00:48:37,881 an extraordinary breadth of possibilities and opportunities. 794 00:48:37,881 --> 00:48:41,385 NARRATOR: Most bipedal hominids went extinct 795 00:48:41,385 --> 00:48:45,389 but one branch went on to evolve larger brains. 796 00:48:45,389 --> 00:48:49,893 That branch eventually led to modern humans. 797 00:48:49,893 --> 00:48:52,896 So how did this crucial transition 798 00:48:52,896 --> 00:48:55,399 to two-legged walking begin? 799 00:48:56,900 --> 00:48:59,903 Liza Shapiro of the University of Texas 800 00:48:59,903 --> 00:49:02,406 looks for clues in living primates. 801 00:49:02,406 --> 00:49:04,408 SHAPIRO: When you look at the fossil record 802 00:49:04,408 --> 00:49:06,910 all you have really is a pile of bones. 803 00:49:06,910 --> 00:49:08,412 It's a nonmoving entity. 804 00:49:08,412 --> 00:49:10,414 There's not much you can know about it 805 00:49:10,414 --> 00:49:12,916 unless you look for living analogs. 806 00:49:14,918 --> 00:49:18,422 So if you look at living animals, you've got the bones 807 00:49:18,422 --> 00:49:21,425 but you can also look at how they're moving. 808 00:49:23,927 --> 00:49:26,930 NARRATOR: In their movements, living lemurs resemble 809 00:49:26,930 --> 00:49:27,931 tree-dwelling primates 810 00:49:27,931 --> 00:49:29,933 that lived up to 50 million years ago. 811 00:49:29,933 --> 00:49:31,935 We didn't evolve from lemurs 812 00:49:32,436 --> 00:49:35,439 but they may be the best living analog 813 00:49:35,439 --> 00:49:38,442 for those distant ancestors. 814 00:49:38,942 --> 00:49:41,945 SHAPIRO: When we're trying to reconstruct the scenario 815 00:49:41,945 --> 00:49:45,449 about how humans evolved bipedally from this ancestor 816 00:49:45,449 --> 00:49:47,951 we have to know what it was we started from 817 00:49:47,951 --> 00:49:51,455 if we're going to come up with an explanation 818 00:49:51,455 --> 00:49:55,459 for not only how we made that transition, but why. 819 00:49:56,960 --> 00:49:59,963 NARRATOR: Today, Shapiro is gathering data 820 00:49:59,963 --> 00:50:02,466 on the movement style of the lemur. 821 00:50:02,466 --> 00:50:05,469 Small reflectors have been gently placed 822 00:50:05,469 --> 00:50:06,970 on the animal's back. 823 00:50:07,471 --> 00:50:10,474 An array of infrared cameras will record the lemur 824 00:50:10,474 --> 00:50:14,478 as it walks across this makeshift bridge. 825 00:50:15,979 --> 00:50:19,483 Of course, getting a lemur to do just about anything on cue 826 00:50:19,483 --> 00:50:20,984 takes a bit of doing. 827 00:50:20,984 --> 00:50:22,986 There you go. 828 00:50:35,499 --> 00:50:38,502 NARRATOR: Finally, the animal makes it across. 829 00:50:38,502 --> 00:50:40,003 Here you go... oh, good! 830 00:50:40,003 --> 00:50:41,505 All right. 831 00:50:41,505 --> 00:50:42,506 Got that. 832 00:50:42,506 --> 00:50:44,007 And he's down. 833 00:50:44,007 --> 00:50:47,511 NARRATOR: The motion of the lemur's spine can now be analyzed 834 00:50:47,511 --> 00:50:50,514 in three dimensions. 835 00:50:50,514 --> 00:50:56,520 The data reveal that lemurs' spines are extremely flexible 836 00:50:56,520 --> 00:51:00,023 capable of many kinds of movements. 837 00:51:00,023 --> 00:51:02,526 SHAPIRO: Lemurs walk quadrupedally 838 00:51:02,526 --> 00:51:04,528 but they're also very good at leaping. 839 00:51:06,029 --> 00:51:10,534 NARRATOR: Like these lemurs, the early primates probably moved 840 00:51:10,534 --> 00:51:12,035 in all sorts of ways: 841 00:51:12,035 --> 00:51:17,541 down on all fours, scampering up trees... 842 00:51:19,042 --> 00:51:22,546 even leaping in an upright position. 843 00:51:24,047 --> 00:51:27,050 They weren't limited to just one style of movement 844 00:51:27,050 --> 00:51:29,553 so they could serve as the starting point 845 00:51:29,553 --> 00:51:32,055 for a number of evolutionary experiments. 846 00:51:35,559 --> 00:51:39,062 And most likely, that's just what happened. 847 00:51:40,564 --> 00:51:42,065 We weren't the only ones 848 00:51:42,065 --> 00:51:44,568 to evolve from those early ancestors. 849 00:51:44,568 --> 00:51:49,072 So did most of today's living primates. 850 00:51:49,072 --> 00:51:53,076 Our closest living relative is the chimpanzee. 851 00:51:53,076 --> 00:51:55,579 We didn't evolve from chimps 852 00:51:55,579 --> 00:51:58,081 but we do share a recent common ancestor. 853 00:51:58,582 --> 00:52:00,083 Can you walk over here? 854 00:52:00,083 --> 00:52:04,087 NARRATOR: That's why our DNA is nearly identical to theirs... 855 00:52:06,089 --> 00:52:09,092 and why our skeletons have the same number of bones 856 00:52:09,092 --> 00:52:11,094 arranged in nearly the same way. 857 00:52:12,596 --> 00:52:16,600 But the few physical differences that set us apart 858 00:52:16,600 --> 00:52:19,603 seem to have made a great difference. 859 00:52:21,104 --> 00:52:24,608 Chimps don't walk on two feet. 860 00:52:24,608 --> 00:52:27,611 They've evolved a different style of getting around 861 00:52:28,111 --> 00:52:29,112 called knucklewalking. 862 00:52:29,112 --> 00:52:30,614 JOHANSON: Knucklewalking 863 00:52:31,114 --> 00:52:34,117 is a very specialized adaptation that we see 864 00:52:34,117 --> 00:52:36,620 among chimps and gorillas today. 865 00:52:36,620 --> 00:52:40,123 It's an adaptation to walking on the ground. 866 00:52:40,123 --> 00:52:44,628 NARRATOR: Knucklewalking was as valid an evolutionary experiment 867 00:52:44,628 --> 00:52:46,129 as two-legged walking. 868 00:52:46,129 --> 00:52:49,132 But the difference in our walking styles 869 00:52:49,132 --> 00:52:52,135 which may have affected our intellects 870 00:52:52,135 --> 00:52:56,139 is seen in the few slight differences in our skeletons. 871 00:52:59,142 --> 00:53:01,645 Here are two skeletons of modern primates. 872 00:53:01,645 --> 00:53:04,147 This skeleton I'm sure you'll all recognize 873 00:53:04,147 --> 00:53:06,650 because it's a skeleton like yours and mine. 874 00:53:06,650 --> 00:53:08,151 This is a modern human. 875 00:53:08,151 --> 00:53:09,653 But this smaller skeleton 876 00:53:09,653 --> 00:53:13,156 is one of our closest living relatives, the chimpanzee. 877 00:53:15,659 --> 00:53:17,160 We began walking on two legs 878 00:53:17,160 --> 00:53:20,664 and that made a whole series of modifications in the skeleton. 879 00:53:20,664 --> 00:53:22,165 In humans, the spinal chord 880 00:53:22,165 --> 00:53:24,668 comes out of the base of the skull 881 00:53:24,668 --> 00:53:26,670 and points straight downwards 882 00:53:26,670 --> 00:53:29,673 rather than coming out of the back of the skull. 883 00:53:29,673 --> 00:53:31,675 The pelvis is shaped very differently. 884 00:53:31,675 --> 00:53:35,679 A chimpanzee has a long, narrow pelvis. 885 00:53:35,679 --> 00:53:38,682 Ours is short and squat. 886 00:53:38,682 --> 00:53:41,184 We walk with our knees close together. 887 00:53:42,686 --> 00:53:46,189 Chimpanzees walk with their knees wide apart. 888 00:53:46,189 --> 00:53:47,691 These are minor differences. 889 00:53:47,691 --> 00:53:51,194 These are the sorts of tinkering that evolution did 890 00:53:51,695 --> 00:53:55,699 to change us into a modern biped. 891 00:53:55,699 --> 00:53:59,703 NARRATOR: What if our ancestors hadn't stood up? 892 00:54:01,204 --> 00:54:04,207 What if they had taken one different turn 893 00:54:04,207 --> 00:54:07,210 along the path to becoming human? 894 00:54:10,213 --> 00:54:15,218 JOHANSON: One of the great misconceptions that most people have is that... 895 00:54:15,218 --> 00:54:19,222 that once our ancestors stood up, it was almost inevitable 896 00:54:19,222 --> 00:54:21,224 that we would be here today 897 00:54:21,224 --> 00:54:24,227 that the egocentric species, Homo sapiens 898 00:54:24,227 --> 00:54:26,229 would evolve in this manner. 899 00:54:26,229 --> 00:54:28,231 But what we see is 900 00:54:28,231 --> 00:54:31,234 that evolution has worked the same way with us 901 00:54:31,234 --> 00:54:34,237 as it has with every, single organism on this planet. 902 00:54:34,738 --> 00:54:38,241 We're here through a series of chance coincidences 903 00:54:38,241 --> 00:54:42,245 specific adaptations, chosen opportunities. 904 00:54:42,245 --> 00:54:45,749 So I think that when we look at our own origins 905 00:54:45,749 --> 00:54:47,751 we see that it is extraordinary 906 00:54:47,751 --> 00:54:51,254 that humans are here to look back and ponder their past. 907 00:54:53,256 --> 00:54:55,258 SHUBIN: Does that mean we are not unique 908 00:54:55,258 --> 00:54:56,259 in many ways? 909 00:54:56,259 --> 00:54:57,761 Of course not. 910 00:54:57,761 --> 00:55:00,263 We're the ones telling this story. 911 00:55:00,263 --> 00:55:02,265 And that's very important... 912 00:55:02,265 --> 00:55:05,268 that evolution, that life has gotten to the point 913 00:55:05,268 --> 00:55:06,770 where it can tell this story. 914 00:55:49,913 --> 00:55:51,414 Continue the journey 915 00:55:51,414 --> 00:55:53,416 into where we're from and where we're going 916 00:55:53,416 --> 00:55:54,918 at the Evolution web site. 917 00:55:54,918 --> 00:55:58,421 Visit www.pbs.org. 918 00:55:58,421 --> 00:56:00,924 The seven-part Evolution boxed set 919 00:56:00,924 --> 00:56:02,425 and the companion book 920 00:56:02,425 --> 00:56:05,428 are available from WGBH Boston Video. 921 00:56:05,428 --> 00:56:11,935 To place an order, please call: