The Evolution of Human Anatomy

From the badlands of Ethiopia to the coasts of Florida, in the bones of ancient creatures and deep inside your own DNA lies an incredible story. The story of your body and why you're built the way you are. You are a cutie. The shape of your hands, your rich color vision, the way you walk, and even the structure of your brain. I mean, I find that mind-blowing. Can all be traced back to ancient primates living in an ancient forest. My name is Neil Shubin. As an anatomist, I look at human bodies differently from most people. Within us, I see the ghosts of animals past. Distant ancestors who shaped our anatomy in surprising ways. Prepare yourself for a trip back to an ancient world. If you really want to know why you look the way you do, it's time to meet your inner monkey. If you go down to your local ice rink, you might not expect to find evidence of your ancient evolutionary past. But if you know how to look, there's a story written in the bodies of these skaters and every one of us. Anyone who's fallen on the ice knows there's one bit of your body you don't want to land on. It's a remnant from a time when our ancestors looked like monkeys, complete with tails. Each of us have a vestige of our tail inside of us. We call that the coccyx, and that sits at the base of our spine. When we fall on that, it really can hurt. And the coccyx is just the beginning. Inside all of us is a record of our ancient primate past. What I like to call an inner monkey. The way we see the world, the way we walk, and even the way we think can all be traced back to a time when our ancestors lived in the trees. If you have a hard time believing we have an inner monkey, try meeting modern-day monkeys face-to-face. In a sense, these guys, squirrel monkeys, are our distant cousins. That is so cool. I mean, it's hard not to look at these guys and feel a deep connection, in a way that you don't feel to fish. You look in their eyes, and you see their hands, and you see the little nails. Now they grab this little nut just like I'm holding it here. I mean it's hard not to feel something powerful connecting you. But the power of that is also scientific. The power of that is in the anatomy, the bones, and also in the body. and the fossils that show us the history we share with them. We're primates. Monkeys and apes and people. But we're all part of the same branch of the tree of life. And all primates are true primates. differ from other mammals in having certain features that other mammals don't have. We have a certain shape to our skull, our eyes face forward. We have a particular kind of hand that can grasp. We share an evolutionary relationship with them. To see what I mean, imagine all life that has ever existed on a giant family tree. From the first microscopic life billions of years ago, to all animals alive today. We didn't evolve from modern monkeys. But if you trace our ancestry back in time, eventually we reach a point Where the human line and the lines of all primates meet. This is where our story begins. Our common ancestor. The ancestor of every monkey, ape, and human alive today. So what did that common ancestor look like? And how has it shaped our own bodies? 1870. The surgeon from the Civil War has returned to his pre-war passion, hunting fossils from the Wild West. In Wyoming territory, he finds a jawbone he thinks might belong to something like a small raccoon. In fact, he's found a creature that lived some 50 million years ago and occupied a place in our family tree very close to the first primates. I've come to meet this creature called Notharctus, and a scientist who knows every inch of its bones, Jonathan Block. This is a 50 million year old primate skeleton. It gives us a window straight into the world of what the earliest primates would have been doing, how they would have been interacting with their environment. Wow. That's the real thing. This is the real deal. That is absolutely exquisite. Like most modern monkeys, Notharctus was a climber, adapted to life in the trees. The evolution of this creature, and others like it, had a huge impact on one of the features that most defines us. Our hands. One of the things that's really nice about this hand is that we do have all of the bones preserved. It's like a jigsaw puzzle, you gotta put it all together to see how that all fits together. It's a three-dimensional jigsaw puzzle. To solve the puzzle of Motharknus'hands, you have to begin even further back in time. Over 365 million years ago, ancient fish used their fins to crawl out of the sea. Those fins evolved into the feet of reptiles, and later into the paws of mammals, with short fingers that all pointed the same way, and claws. Early primates like Notharctus took the mammalian hand to a whole new level. One that seems very familiar to us. When you actually articulate all of these bones, what you see is that the thumb is divergent. That is, it forms an angle with the index finger. And so that shows you that it could bring its thumb into opposition with the rest of the digits. Netharctus also has unusually long fingers and nails instead of claws. This is one of the first times in the fossil record that we see a hand that looks like our own. The hand of a primate. It's a turning point in the story of the human body. An anatomical change that would eventually let us shape the world around us. So what were early primates doing with these new hands? To find out, I'm going up into the habitat where my ancient ancestors actually lived, up in the trees. Thankfully, I've got ropes. Minor monkey's not what it used to be. Okay, ready? Yeah, there you go. There you got it. Natural. A little knotty up here. Just push your hand jammer a bit higher so you can pull the rope through your crop. Woo-hoo! Thank you, Jim. This is utterly wild. I mean, I was never a real climber as a kid. And I have to admit, I'm a little scared of heights and uncomfortable in trees. But these creatures are so unbelievably agile all through here. This is their home. They are able to... to live on small branches, big branches, throughout the tree. They can jump branch to branch. You know, when you're in the tree, what you see is that the canopy is not one place. There are lots of environments, lots of niches up here. And one special one is on the ends of the branches, because it's there where the flowers and the fruits and the insects are. So the rewards are great to be out there. We call it the fine branch niche. And for the earliest primates, being able to get out there would have been really important. And that gives us a clue as to why their hands and feet evolved to be so different from what came before. Creatures with really short fingers and claws, they're really great at crawling these big, thick branches, but not so much when you get to the ends of the branches. That's because this sort of hand can't grasp. Lengthening the fingers, and better still, adding a divergent thumb, means you can curl your fingers around even the thinnest branches, grasp them tight, and remain stable. We think that's why the hands and feet of early mammals changed. What you end up with are primate hands, wonderfully adapted to moving around the fine branches of trees. Embedded in our bodies is our distant past. The hand I used to write with, to type onto the computer, to throw a baseball, that hand has a long evolutionary history. And one important point in that history was here in the trees, on the fine branches, that made a hand with longer fingers and a thumb. Life in the trees would lead to another critical change in our ancestors'bodies. A change deep within their eyes, as they began to see the world in rich color. I first got interested in the evolution of color vision back in 2009. I was watching my two kids, Nathaniel and Hannah, playing a game called Hiss, where they matched cards of a certain color to make a snake. Nathaniel's, you know, buff. He's three and a half years older than Hannah. He should whoop her, right? But he consistently lost. And he would lose because he'd make mistakes with one kind of card, which was purple and blue. And then we realized Nathaniel's likely colorblind. In a sense, he sees the world like early primates did before they evolved our rich color vision. Nathaniel can only see a limited range of yellows and blues, and can't tell the difference between reds, greens, and purples. This means he's not so great at games like his. But it doesn't affect his life much more than that. And it certainly doesn't affect his ability to find food or to survive to adulthood. That wasn't the case for our primate ancestors. For millions of years, they'd been unable to tell the difference between fine shades of red and green. Then, about 23 million years ago, one group of primates evolved the ability to see many more colors. Now they could tell the difference between ripe red fruits and unripe green fruits and spot the most nutritious leaves. In the evolutionary battle for survival, this would have been a big advantage. So what happened to the eyes of our ancestors? How did our rich color vision evolve? To help me answer those questions, I've come to Seattle to meet one of the world's experts on color vision, Jane Knights. Oh, hey, Neil Shubin. Hey, great to meet you. Good to see you. Well, great to be in the color lab. Well, thank you. Well, I think we're off to a rockin'start with these walls. This is the color lab. Yes, it is. So what's the drill here? Jay's been studying color vision for the last 25 years. He combines cutting-edge genetics with studies on humans and other primates. Everything is cool about color vision. It's a silent language that speaks to our emotions. And it's just fascinating. This is the place, huh? Yep. This is where we test color vision in the monkeys. His work helped scientists figure out that most mammals, including most primates, see a limited range of colors. This is Kramer. Hi, Kramer. And Kramer is red-green colorblind, but he has good blue-yellow color vision. In order to train that, them, we use the colors that they can see. So as you can see, that here is this yellow blob against a gray background. Kramer can see that as well as we can. If they get it right, they get a little reward, and they also get a clicking sound. Oh, he clearly was trying to kiss it there. He really did. He went, bop! You can see how good he is at it. He is. Kramer aces this first test. You've done really well there, Kramer. Change the colors to red and green. and it's a whole different ballgame. If you don't have any color vision, this is completely invisible. If you can't see red or green, this just looks like a totally gray background. Most humans Can clearly see this red blob, but Kramer can't. Like my son Nathaniel, he can't tell the difference between reds and greens. Okay Kramer, you are a star. So why is this happening? Why doesn't Kramer see the world like we do? Kramer's eyes, like all eyes, rely on special proteins called opsins to detect color. They're held in thousands of special cells in the retina in the back of the eye. Kramer's got two types of opsins, each tuned to specific wavelengths of light. Signals from these opsins are then interpreted by the brain, which allows us to perceive color. But to see color like we do, Kramer would need a third opsin, tuned to different wavelengths of light. We think our early primate ancestors were like Kramer. They had just two opsins as well. So how did they evolve a third opsin? The answer is in our DNA. Each opsin is encoded by a single gene. And when scientists compared these genes, they found that the gene for the newer opsin sits right next to one of the old ones. And significantly, they are incredibly similar. Both facts are telltale clues as to how the extra gene evolved. The old Opsin gene must have been duplicated. And one of these copies then acquired a small number of mutations that allowed it to detect different wavelengths of light. But there's one more question. Could our rich color vision result from just duplicating a gene? Or would there have to be changes to the brain as well? To find out, Jay has tried to replicate what happened in nature in his lab. It's actually a great evolutionary question. How did color vision evolve? How can something so complicated evolve? Jay implanted a third opsin gene from a human. directly into the retinas of a colorblind squirrel monkey called Sam. What we did is really a test to see what's the minimal thing you could do in order to give an animal color vision. The results were incredible. Like Kramer, Sam used to fail this test. Now he can easily tell the difference between reds and greens. Jay has recreated evolutionary history and given Sam human-like color vision. You might think, oh it would take him a long time to learn this new pattern in the brain. As soon as the gene was turned on, the animal began to make these discriminations that they couldn't make before. The brain was already ready somehow. And so in one, you know, very short evolutionary step, it goes to this totally different world. You go from just having strictly, let's say five colors, gray, black, white, blue and yellow. to hundreds of different colors that are all the blues and greens and purples and oranges. One simple shift opens the whole universe of colors. Yeah, that's the amazing thing. It's like there's something almost magical. It's a multiplicative effect. For the early primates that evolved this ability, it was a huge advantage, one that would eventually be passed on to us. And color still plays a huge part in our lives today. Color helps us communicate, attract attention, and even express emotions. We often take it for granted, but it massively enriches our experience of the world. Good boy. But our focus on vision has come with some trade-offs, namely, our poor sense of smell. Like most humans, I'm experiencing this wonderful vista here with my eyes. But the dog's experiencing this in a very different way. This is a world of smells. We think that a dog's sense of smell is anywhere from a thousand to a million times better than ours. Like many mammals, it's his main way of understanding the world around him. This fundamental difference in our sense of smell is also reflected in our DNA. A dog has about a thousand genes that are devoted to detecting odors. We have roughly the same number, but about 600 of them don't work anymore. They're relics. It's a similar story in other primates with color vision. These broken genes reveal another legacy of our primate past. As our distant ancestors gained this wonderfully rich sense of color vision, what happened was our sense of smell became less important. And in the evolutionary world, it's use it or lose it. And that's exactly what happened to our sense of smell. It diminished over time. So while we can thank our inner monkey for our wonderful color vision, we can also blame it for our lousy sense of smell. Of course, we humans have also made some radical changes to the ancient primate body plan. Unlike monkeys, we stand up on our own two feet. You know, animals have been walking on this planet for over 365 million years, and for the most part that walking has been on four legs. Walking on two legs is a fundamentally strange way to get around. No other primate, and very few other mammals move this way. It's a change that had profound effects on the human body. Which begs the question, how on earth did it happen? The best place in the world to answer this question is in Africa. A site where the Great Rift Valley cuts deep into ancient rocks, exposing fossils from our distant past. These are the remote badlands of northern Ethiopia. Look at those rocks, they're boom, boom, boom, boom, boom, just totally stretched out. As a paleontologist, that is what I dream about. This is truly in the middle of nothing. Now see the volcanic ash dropping out? That's 3.4 million years old. That is incredible. My guide is Don Johansen, one of the first people to hunt for fossils here back in the early 70s and a childhood hero of mine. There's the camp. They're on the far side of the river right there. Two of the most important fossils for understanding the origins of bipedalism have been found in this small region of Ethiopia. Don's taking me to see where the first iconic fossil was found. A 3.2 million year old human ancestor known as Lucy. It was a Sunday morning back in 1974. So I came up here, looked at this, had no idea what was waiting. It was right in this area, right here. What I saw was a fragment of bone, and I looked at it and almost instantaneously said, that's a hominid. Wow. Lucy made headlines around the world because although she looked like an ape she walked on two legs she was a biped at that stage the most ancient anyone had found once we broke that three million year barrier it was a whole new picture of what our earliest ancestors looked like the one of the most exciting moments of my my entire career Since dawn first came here in the 70s, scientists have organized expeditions here most years. They found over 400 individual fossils from Lucy's species. But it's Lucy I most want to meet. Her bones are some of the best evidence we have for what early bipeds looked like. Now of course if this were all articulated properly, you know, with the vertebra on top of it, she'd be about three and a half feet tall. You don't see that. Yeah, you don't get that. Here's the femur. That's the left. Top end of the thigh bone. And this one also, when you put it all together, now you have... you know this is telling bipedal this is giving a hint of bipedal this certainly tells it was bipedal that kids in like that which is very characteristic our knees are close together they have to decide chimps come straight up having the upper and lower leg in a straight line is no good for a biped it makes for an awkward waddling game Lucy's legs formed an angle. Her knees were closer together, just like our own knees. This positions the feet directly underneath the body, making walking easier and more efficient. So Lucy walked much like us. But she wasn't human. She had many primitive features, too. This is a real mix, you know. This is a real mix. Yeah, it's amazing. This is very primitive, right? Ape-like. Very small brain. And very ape-like proportions. Bipedal. Bipedal. Cool. And these hands would have stretched down to about here. So down, yeah, to the neomar. It's just so utterly fabulous. Isn't it interesting they had the pile of bones, you put her here and all of a sudden you can see that it was a living person. She's beautiful. Yep. Thank you. We named her after the people and the land. We named her Australopithecus afarensis, from the Afar region. So imagine if Lucy was here with us right now. What would she look like? Well, she'd be short. She's only about 3 and 1 half feet tall. And the one thing that would be familiar to us, she would be walking upright. With those long, arms reaching almost down to her knees. She probably had a very odd gait. And as she got closer, we'd see that she had a very ape-like face. I don't think you would see much of a glimpse. of philosophical thought with her eyes. I think in many ways she looked like the ape that stood up. Yeah. You know? That's amazing. Lucy tells us that by 3.2 million years ago, our ancestors had fully committed to walking on two legs. What she can't tell us is how our ancestors first started walking upright. To answer that question, we need to meet a second iconic fossil, found just 50 miles from the Lucy site. This fossil, called Ardipithecus, has turned our ideas about how we became bipedal on their head. I've come to Berkeley, California to meet the guy who led the team that discovered ARTIE, an old colleague of mine, Tim White. Tim's out in the field in Ethiopia most years, and he documents his work meticulously with a video camera. These rarely seen field tapes date from the early 90s. What we wanted to do was to plumb the unknown, to figure out what came before the Lucy species. We just literally didn't know what we would find. Since 1992, the team has run annual expeditions to a remote site called the Middle Awash. Some of the rocks here were millions of years older than the nearby Lucy site. You see the two resistant bands up there on the hill, they're digging into the lower band. Both of these are dated to 4.4 million. This was really... We nailed it. So anything between that is 4.4 million years. This band of ancient rock yielded some tantalizing fragments. So they scoured this layer for months on end. The breakthrough finally came in 1994. An Ethiopian graduate student, Yohannes Helisilasi, found a fragment of hand bone in that same layer. He picked up and said, this looks like a hominid. So we scraped and brushed that surface, and we found some of these hominid hand and foot bones in place. And so we focused on that little hill. And we turned the video camera on and dug. Oh, wow. This is the way we took it off, virtually a millimeter at a time. You've got to be really careful. You scratch that, you put your signature on it forever. Here comes the mandible. Canine's off on the left-hand side right there. Here are the teeth coming out. You know, so as a paleontologist, you're the first people in the entire planet to see that. That's been buried for 4.4 million years. This was a hugely significant find. A new species of hominid at a critical moment in human evolution. A time when our ancestors were just beginning to walk on two legs. So while they were still in the field, Tim wanted to collect as much information as he could about Artie's world. What we're out to do is to understand everything we can about that time slice. And at 4.4 million years, anything we learn is new. And so that means bringing in... Sedimentologists who understand what kind of a setting, was it a river, was it a floodplain, bringing in paleontologists expert in the plants, in the birds, in the shrews. Wherever they found arty species, they found woodland creatures, parrots, monkeys and peacocks, as well as woodland plants. It was a woodland, not an open savanna setting. Now that's a surprise. These are woodland animals. That runs counter too. So much of what runs canter all the way back to the 1800s For over a hundred years. There's been one main theory of how our ancestors started to walk on two legs The theory goes like this we started out as apes that lived in the trees We looked like chimpanzees and walked on all fours using the knuckles of our hands, but the climate changed And only after Forest had turned to Savannah did we start walking on two legs instead of four. Artie tells a very different story. She was already walking upright while living in the woodlands. Artie's skeleton ran counter to the old theory too. It was unlike anything anyone had seen before. It took a team of experts 15 years to fully piece her together. So how do we know she was bipedal? The man in charge of figuring out how Artie might have moved was anatomist Owen Lovejoy. The critical thing in bipedality is the structure of the pelvis. And at first when you look at this bone, you might think that there's not much information here. But actually there's an enormous amount of information that tells you a great deal about what the original bone looked like. Using information from this deformed bone, the team was able to find out able to reconstruct Artie's entire pelvis. This is a plastic structure that's produced by a three-dimensional printer. The top part of Artie's pelvis looks more human. The hip bone is short and broad, a key indicator of bipedalism. But the lower half is much longer than a human pelvis, more useful for climbing. When you got to that detail, you realized it was a mosaic of anatomy that had never been encountered before. It suggests that Artie could walk on two legs, but not as well as later hominids like Lucy. And the rest of her anatomy held surprises too. Neither Lucy nor humans have the ability to grasp with their big toe, but this thing had full grasping ability. So she has a grasping foot that can walk? Yes. Even the hands were a mosaic. Incredibly long fingers, good for climbing, but a shorter human-like palm. And the bones show none of the telltale signs that she walked on her knuckles like a chimpanzee. So we now have a detailed picture of the crucial time when our ancestors had just started walking on two legs. Hardy was small, around four feet tall. A good climber, she moved on all fours when in the trees, but she walked upright when on the ground. She blows the old theory of how we became bipedal out of the water. Not only did our ancestors start walking on two legs when still living in the woods, they never looked or moved like our closest living relative, the chimpanzee. Some scientists don't accept this interpretation. They think Artie isn't a human ancestor at all, but the relic of an extinct ape. But Tim's spent years studying many specimens of Ardipithecus, and he thinks the evidence is clear. When we looked at the Ardi cranium, we saw very small canines. No other ape, living or fossil, has such reduced canines. That's a good indicator. She's come in our direction a bit. Go to the pelvis, same thing. A unique adaptation shared by humans and Lucy. We're still not sure exactly why a woodland climber needed to walk on two legs. But thanks to ARTIE, we now have a snapshot of one of the most dramatic transformations in the history of our species. The transition from walking on four legs to walking on two. This major change to our ancestral body plan has serious consequences for us today. These consequences can be seen within our own bodies, and they're not all good. This vault in the bowels of the Cleveland Museum of Natural History is the place to go if you want to find out what can go wrong with the human skeleton. Dr. Bruce Latimer is an anthropologist and anatomist who was a curator here for many years. Well, this is the Hammond-Todd collection, which is the largest collection of its type in the world. There are over 3,000 skeletons in this room. In each one of these drawers is a complete human skeleton. They come from unclaimed bodies at a Cleveland morgue dating from the early 1900s. If you study these skeletons, one thing becomes clear pretty quickly. The human back goes wrong. A lot. There's an enormous amount of back problems. The pain must have been phenomenal. And you just see that all over this collection. Turns out, our bad backs are an unwelcome inheritance from our inner monkey. We took a skeleton like this that was essentially horizontal. We stood it upright. We've had to change essentially every bone to allow us to do that. And we forced it into this new position. We have a problem going from this kind of animal into that kind of animal, and our main problem is balance. On all fours, the weight of our body hangs down from our spine. But turn this body upright, and the weight is all out front. It puts us out of whack, totally out of balance. In order to balance, we had to create this curve on your back. And then, your head would be back here, wouldn't it? So we had to create another curve here in the middle of your chest, and then your head would be sticking out in the front, so we had to create another curve in your neck. So we have this S-shaped curve in our spine, and we expect that to hold us up. That is an engineering nightmare. Our S-shaped spine is unique among mammals, and it causes all sorts of problems. The vertebrae that make up the bones of your back, and the discs between them, are put under a lot of pressure, particularly the ones at the very apex of the biggest curve, the thoracic vertebrae. If you take those thoracic vertebrae and you push on them from the ends too hard, what happens is this. You end up with what's called a wedge fracture. That curve has crunched it. No other animal has anything even remotely like this. It's a consequence of how we walk. And it's not just fractured vertebrae. From slip discs to sciatica, our spines go wrong in all kinds of ways. 80% of all Americans will complain of back problems at some point in their lives. Our inner monkey has a lot to answer for. But I don't want you to get the wrong idea. Standing up on two legs wasn't all bad, or it never would have happened in the first place. It freed our hands, an anatomical change that, combined with our amazing brains, would eventually allow us to make tools and reshape the world around us. This key moment in our evolutionary history is once again visible in the rocks of northern Ethiopia. So geologically, one of the things that's special about this is it has lots of layers. Lucy's from one part of it, and we're going to another, right? That's right. We've just jumped about 600,000 or 700,000 years in time. And that is kind of mind-blowing. Yeah. Paleontologist Bill Kimball has brought me to a site where you can find stone tools that are over 2 million years old. If you know what you're looking for. for so what do I look for well you'll look for flakes on the ground what was that bone that is a piece of fossil bone and here's another one can't find tool like if I'm bone yeah yeah the important thing about tools is it's the hand and the brain right it's it's it's both together absolutely you got one this is very typically nice one I don't get this at all yeah I know it looks like something from your driveway the tool Don's found was made by human ancestors called homo habilis who lived a million years later than lucy clearly some early human took a stone a hammer stone and struck it right there and got oh yeah you got striated field that edge You could use it to strip off meat or whatever. So from this rock you can tell where they hid it, how they hid it. It's almost like a time machine you have. It is. It's a time machine that takes us back to a period when the faintest glimmers of what it means to be human are beginning to emerge. The use of the hand, the cognition, the repeated behavior to produce a stylized tool. It's mind blowing. Wow. Can we look for tools? I want to find a tool. No, that's natural. No, this is one. You found one. Making tools takes excellent vision, fine motor skills, and a brain that can integrate the two. We humans only have this sort of brain because it's been shaped by our ancient primate past. Monkey, ape, or human, our brains share a basic architecture that's different from most other mammals. We all have a special region involved with hand-eye coordination. And a greatly expanded visual system with as much as 40% of the brain involved in seeing. Our inner monkey hasn't just shaped our bodies, it's shaped our brains as well. But if you look at the modern world around us, and everything humans have been able to build, from satellites to skyscrapers, there's no doubt we're more intelligent than monkeys. So what changed? What made our brains so different from those of other primates? Hi, Neil Schuman. Hi, Neil. This is Tom Burbacher. Welcome to the infant primate lab. So this is the monkey place, huh? This is the monkey place. Tom Burbacher studies monkeys in order to answer questions about our own brains. He's going to show me an experiment that demonstrates an important difference between our brains and the brains of a monkey. But the differences aren't what you might expect, especially when we're young. Monkey on the set. Monkey on the set. Neil, this is CI. She's a three-month-old pigtail macaque. This experiment tests something called object permanence. In other words, whether this monkey knows an object still exists when she can't see it. It's a developmental milestone for both monkeys and humans. You're going to put a piece of fruit on the toy itself. You'll place it in the well. She's looking at it. There. And you'll move that to completely hide that toy. Okay. There you go. Wow! There you go. Wow! That is impressive. Object permanence. Boom, boom. Three months old, and already CI understands object permanence. CI, you are good. Hi Geneva, how are you? You are a cutie. Geneva is the same age as the baby monkey. I'm going to do the exact same test on her under the expert eye of child development specialist, Professor Susan Speaker. She needs to reach for him, show that she's interested. Oh, I think we got interest. She's got a good reach. You do, look at you. Oh, Geneva, you like those. Hello! Now, Neil, can you get them away? Oh, I'm an expert at this. Can I take that for a sec? Sorry, it's temporary. You are so good that way. I'll pop it in. Make sure she's watching. She's watching. We'll cover it up, watch this. And she wonders, what did you do, Neil? What toys? I don't know where they went. Wow, that is amazing. Where did they go? It is incredible. If it's not there, it doesn't exist. Right. That is amazing. So how come a baby monkey beats a baby human in this test? These tests are showing us how rapidly a particular region of our brain is wiring up in development. And it's showing us comparatively that we wire up much slower in this part of the brain than do monkeys. Compared to other primates, we humans have an unusually long childhood, even if you take the different lifespans into account. This should be an evolutionary disadvantage. But in fact, it's one of our greatest strengths. During childhood, our brains are being shaped by our environment and by our experience. Extending this phase gives us longer to learn and pick up new skills. Some think that this is a key part of what makes us so smart. But there are other factors too. The brain is made up of vast networks of nerve cells called neurons that carry, process, and store information. The part of the human brain responsible for higher thought, the cortex, contains more neurons than that of any other animal on the planet. An astonishing 16 billion. These neurons are organized in a uniquely powerful way. They're unusually interconnected. This means we can do things that other primates can't. Build complex tools, compose symphonies, and even investigate how our own brains work. But before we get too carried away with our own cleverness, I want to inject a bit of humility. That means leaving monkeys behind and going back to where the series began. My anatomy lab in Chicago and my favorite subject, fish. The brain of a fish and the brain of a human have more in common than you might think. This is a trip to the beginning. This is as basic as it gets. We're going human fish represented by a cartilaginous fish, a shark on the right. And what you have is you see the muscles and nerves and organs inside the shark head. But importantly you see this yellow tissue. This is the front end of the of the spinal cord. It's the brain. Doesn't look like much but it's the shark brain. This is the human brain. This is where it all happens for us. Where our memories reside. Where our, you know, our fears, our loves, our hates. It's all in here. The human brain, really, at the surface level, looks nothing like what's sitting inside the shark head. Yet when you know how to look, you find a very... profound similarity and that similarity lies in the overall architecture of the brain itself in the human we have a forebrain and that forebrain consists of this folded tissue here or much of our conscious thought happens and then there's a midbrain this walnut sized area in the middle And then a hindbrain. That's a fundamental division. We see that in development, and we see that based on where the nerves exit the brain. Well, if you follow the similar nerves in a shark, what you see is sharks, too, have that same structure. A forebrain, a midbrain, and a hindbrain. There's a fundamental architectural similarity among all brains. The brains of people, the brains of dogs, the brains of cats, the brains of monkeys, lizards, frogs, salamanders, trout, bass, even sharks and fish are similar. Each one of them has a forebrain and a midbrain and a hindbrain, despite the fact that those brains are often very different in function and form. But that's not the end of the story. The fundamental architecture of our own brains can be traced back even further than fish, to a surprisingly primitive animal that doesn't even really have a brain. But I've got to find these tiny creatures. first. All right, OK. Well, we could start trying around here. Thanks, Master Spock. Thanks, Master Spock. Let's give it a go. This is Peter Holland, a world-renowned geneticist and head of zoology at Oxford University in England. Okay, so what do I do? Just shake it. Shake and bake, huh? I'll make it look so easy. That? No. That'll be pretty obvious because they'll really swim around. The water makes the digging slightly harder. It does. You got one. There's an amphioxid. We got any? Whoa, look at that little guy go. Hey! Just dip it in the water again, you'll see it. Well, they really flick. There he is. Hey, that's beautiful. Look at that. Which is the front? It doesn't look like much, but this tiny creature called amphioxus has much to tell us about our own brains. That is cool. Okay, that ranks as cool. Okay, so let's take a look at a couple of these. So I brought this from the anatomy lab in Chicago. This is a human brain. When I look at this, I don't find any obvious similarities to that. Deep in the genes of this animal and the development of this animal and deep in the genes of us and the development of us, there are the similarities. They're pretty active. Holy cow. Oh, that is beautiful. God, they're so clear, too. You can see right through them. That's amazing. Amphioxus lives in the sand of the ocean floor, filtering algae out of the water. It's from an incredibly ancient group of animals. We found fossils that look a lot like... This and rocks that are over 500 million years old. They are a window into what came before the first fish. And crucially, they don't have anything like what we'd call a brain. The simple nerve cord that runs the length of their body ends with just a tiny swelling invisible to the naked eye. If you look at the front end of this animal, you don't see it all expanded into a large skull or brain region. It's just pointed. But if you look at the genetic makeup of these ancient creatures, you find something truly remarkable. To make the forebrain, midbrain, and hindbrain that we saw in our lab, you need a series of control genes to tell the cells within the developing brain where they are. They're like a zip code. Those same control genes that make our own brains are active in Amphioxus. But here, they're simply building the primitive nerve cord and the tiny swelling at its front. This means that the genetic roots of our complex primate brains existed in much simpler creatures that first arose over 500 million years ago. I think it gives us a glimpse into where our brains came from. Into the basic organization of the brain of our ancestors. I mean, I find that mind-blowing. He's just an exciting animal. He knows you're talking about him. See, he's going. That's right. He's going. You can see that. muscle blocks really working that um yeah and i think to an evolutionary but well he's oh sorry he's going uh tectonic on this he's going land living uh he's got a road yeah he's gone for the next transition exactly he's in the devonian now The search for our inner fish has taken me from high in the Arctic Here was the snout of exactly the creature we were looking for to the plains of Africa Yeah, I just want to run down here and start collecting fossils Let's go as well as deep inside our own DNA And today we saw a little tiny worm living in the mud here in the bay that contains genes that we have that sculpt our own brains. The organ that gives us many of our unique properties. We've seen how our distant relatives, from worms to fish, from reptiles to early primates, have defined our bodies. At each new stage of our journey along the tree of life, our ancient animal ancestors have reconfigured what's gone before. And that's how we ended up as the intelligent creatures with all our quirky flaws that dominate the planet today. There's something incredibly profound, and I think beautiful, in the idea that inside every organ, cell, and gene of our body lie deep connections to the rest of life on our planet.

The shape of your hands, your rich color vision, the way you walk, and even the structure of your brain. I mean, I find that mind-blowing. Can all be traced back to ancient primates living in an ancient forest.

My name is Neil Shubin. As an anatomist, I look at human bodies differently from most people. Within us, I see the ghosts of animals past. Distant ancestors who shaped our anatomy in surprising ways.

Prepare yourself for a trip back to an ancient world. If you really want to know why you look the way you do, it's time to meet your inner monkey. If you go down to your local ice rink, you might not expect to find evidence of your ancient evolutionary past. But if you know how to look, there's a story written in the bodies of these skaters and every one of us.

Anyone who's fallen on the ice knows there's one bit of your body you don't want to land on. It's a remnant from a time when our ancestors looked like monkeys, complete with tails. Each of us have a vestige of our tail inside of us.

We call that the coccyx, and that sits at the base of our spine. When we fall on that, it really can hurt. And the coccyx is just the beginning.

Inside all of us is a record of our ancient primate past. What I like to call an inner monkey. The way we see the world, the way we walk, and even the way we think can all be traced back to a time when our ancestors lived in the trees. If you have a hard time believing we have an inner monkey, try meeting modern-day monkeys face-to-face. In a sense, these guys, squirrel monkeys, are our distant cousins.

That is so cool. I mean, it's hard not to look at these guys and feel a deep connection, in a way that you don't feel to fish. You look in their eyes, and you see their hands, and you see the little nails.

Now they grab this little nut just like I'm holding it here. I mean it's hard not to feel something powerful connecting you. But the power of that is also scientific. The power of that is in the anatomy, the bones, and also in the body.

and the fossils that show us the history we share with them. We're primates. Monkeys and apes and people.

But we're all part of the same branch of the tree of life. And all primates are true primates. differ from other mammals in having certain features that other mammals don't have. We have a certain shape to our skull, our eyes face forward. We have a particular kind of hand that can grasp.

We share an evolutionary relationship with them. To see what I mean, imagine all life that has ever existed on a giant family tree. From the first microscopic life billions of years ago, to all animals alive today. We didn't evolve from modern monkeys.

But if you trace our ancestry back in time, eventually we reach a point Where the human line and the lines of all primates meet. This is where our story begins. Our common ancestor. The ancestor of every monkey, ape, and human alive today. So what did that common ancestor look like?

And how has it shaped our own bodies? 1870. The surgeon from the Civil War has returned to his pre-war passion, hunting fossils from the Wild West. In Wyoming territory, he finds a jawbone he thinks might belong to something like a small raccoon. In fact, he's found a creature that lived some 50 million years ago and occupied a place in our family tree very close to the first primates.

I've come to meet this creature called Notharctus, and a scientist who knows every inch of its bones, Jonathan Block. This is a 50 million year old primate skeleton. It gives us a window straight into the world of what the earliest primates would have been doing, how they would have been interacting with their environment. Wow.

That's the real thing. This is the real deal. That is absolutely exquisite.

Like most modern monkeys, Notharctus was a climber, adapted to life in the trees. The evolution of this creature, and others like it, had a huge impact on one of the features that most defines us. Our hands. One of the things that's really nice about this hand is that we do have all of the bones preserved. It's like a jigsaw puzzle, you gotta put it all together to see how that all fits together.

It's a three-dimensional jigsaw puzzle. To solve the puzzle of Motharknus'hands, you have to begin even further back in time. Over 365 million years ago, ancient fish used their fins to crawl out of the sea. Those fins evolved into the feet of reptiles, and later into the paws of mammals, with short fingers that all pointed the same way, and claws. Early primates like Notharctus took the mammalian hand to a whole new level.

One that seems very familiar to us. When you actually articulate all of these bones, what you see is that the thumb is divergent. That is, it forms an angle with the index finger. And so that shows you that it could bring its thumb into opposition with the rest of the digits. Netharctus also has unusually long fingers and nails instead of claws.

This is one of the first times in the fossil record that we see a hand that looks like our own. The hand of a primate. It's a turning point in the story of the human body. An anatomical change that would eventually let us shape the world around us. So what were early primates doing with these new hands?

To find out, I'm going up into the habitat where my ancient ancestors actually lived, up in the trees. Thankfully, I've got ropes. Minor monkey's not what it used to be. Okay, ready? Yeah, there you go.

There you got it. Natural. A little knotty up here. Just push your hand jammer a bit higher so you can pull the rope through your crop.

Woo-hoo! Thank you, Jim. This is utterly wild.

I mean, I was never a real climber as a kid. And I have to admit, I'm a little scared of heights and uncomfortable in trees. But these creatures are so unbelievably agile all through here. This is their home.

They are able to... to live on small branches, big branches, throughout the tree. They can jump branch to branch. You know, when you're in the tree, what you see is that the canopy is not one place.

There are lots of environments, lots of niches up here. And one special one is on the ends of the branches, because it's there where the flowers and the fruits and the insects are. So the rewards are great to be out there.

We call it the fine branch niche. And for the earliest primates, being able to get out there would have been really important. And that gives us a clue as to why their hands and feet evolved to be so different from what came before. Creatures with really short fingers and claws, they're really great at crawling these big, thick branches, but not so much when you get to the ends of the branches. That's because this sort of hand can't grasp.

Lengthening the fingers, and better still, adding a divergent thumb, means you can curl your fingers around even the thinnest branches, grasp them tight, and remain stable. We think that's why the hands and feet of early mammals changed. What you end up with are primate hands, wonderfully adapted to moving around the fine branches of trees.

Embedded in our bodies is our distant past. The hand I used to write with, to type onto the computer, to throw a baseball, that hand has a long evolutionary history. And one important point in that history was here in the trees, on the fine branches, that made a hand with longer fingers and a thumb.

Life in the trees would lead to another critical change in our ancestors'bodies. A change deep within their eyes, as they began to see the world in rich color. I first got interested in the evolution of color vision back in 2009. I was watching my two kids, Nathaniel and Hannah, playing a game called Hiss, where they matched cards of a certain color to make a snake. Nathaniel's, you know, buff.

He's three and a half years older than Hannah. He should whoop her, right? But he consistently lost. And he would lose because he'd make mistakes with one kind of card, which was purple and blue. And then we realized Nathaniel's likely colorblind.

In a sense, he sees the world like early primates did before they evolved our rich color vision. Nathaniel can only see a limited range of yellows and blues, and can't tell the difference between reds, greens, and purples. This means he's not so great at games like his. But it doesn't affect his life much more than that.

And it certainly doesn't affect his ability to find food or to survive to adulthood. That wasn't the case for our primate ancestors. For millions of years, they'd been unable to tell the difference between fine shades of red and green. Then, about 23 million years ago, one group of primates evolved the ability to see many more colors.

Now they could tell the difference between ripe red fruits and unripe green fruits and spot the most nutritious leaves. In the evolutionary battle for survival, this would have been a big advantage. So what happened to the eyes of our ancestors?

How did our rich color vision evolve? To help me answer those questions, I've come to Seattle to meet one of the world's experts on color vision, Jane Knights. Oh, hey, Neil Shubin.

Hey, great to meet you. Good to see you. Well, great to be in the color lab.

Well, thank you. Well, I think we're off to a rockin'start with these walls. This is the color lab. Yes, it is.

So what's the drill here? Jay's been studying color vision for the last 25 years. He combines cutting-edge genetics with studies on humans and other primates. Everything is cool about color vision.

It's a silent language that speaks to our emotions. And it's just fascinating. This is the place, huh? Yep. This is where we test color vision in the monkeys.

His work helped scientists figure out that most mammals, including most primates, see a limited range of colors. This is Kramer. Hi, Kramer. And Kramer is red-green colorblind, but he has good blue-yellow color vision.

In order to train that, them, we use the colors that they can see. So as you can see, that here is this yellow blob against a gray background. Kramer can see that as well as we can.

If they get it right, they get a little reward, and they also get a clicking sound. Oh, he clearly was trying to kiss it there. He really did.

He went, bop! You can see how good he is at it. He is. Kramer aces this first test. You've done really well there, Kramer.

Change the colors to red and green. and it's a whole different ballgame. If you don't have any color vision, this is completely invisible.

If you can't see red or green, this just looks like a totally gray background. Most humans Can clearly see this red blob, but Kramer can't. Like my son Nathaniel, he can't tell the difference between reds and greens. Okay Kramer, you are a star. So why is this happening?

Why doesn't Kramer see the world like we do? Kramer's eyes, like all eyes, rely on special proteins called opsins to detect color. They're held in thousands of special cells in the retina in the back of the eye.

Kramer's got two types of opsins, each tuned to specific wavelengths of light. Signals from these opsins are then interpreted by the brain, which allows us to perceive color. But to see color like we do, Kramer would need a third opsin, tuned to different wavelengths of light.

We think our early primate ancestors were like Kramer. They had just two opsins as well. So how did they evolve a third opsin?

The answer is in our DNA. Each opsin is encoded by a single gene. And when scientists compared these genes, they found that the gene for the newer opsin sits right next to one of the old ones.

And significantly, they are incredibly similar. Both facts are telltale clues as to how the extra gene evolved. The old Opsin gene must have been duplicated.

And one of these copies then acquired a small number of mutations that allowed it to detect different wavelengths of light. But there's one more question. Could our rich color vision result from just duplicating a gene?

Or would there have to be changes to the brain as well? To find out, Jay has tried to replicate what happened in nature in his lab. It's actually a great evolutionary question. How did color vision evolve?

How can something so complicated evolve? Jay implanted a third opsin gene from a human. directly into the retinas of a colorblind squirrel monkey called Sam.

What we did is really a test to see what's the minimal thing you could do in order to give an animal color vision. The results were incredible. Like Kramer, Sam used to fail this test. Now he can easily tell the difference between reds and greens.

Jay has recreated evolutionary history and given Sam human-like color vision. You might think, oh it would take him a long time to learn this new pattern in the brain. As soon as the gene was turned on, the animal began to make these discriminations that they couldn't make before. The brain was already ready somehow.

And so in one, you know, very short evolutionary step, it goes to this totally different world. You go from just having strictly, let's say five colors, gray, black, white, blue and yellow. to hundreds of different colors that are all the blues and greens and purples and oranges. One simple shift opens the whole universe of colors. Yeah, that's the amazing thing.

It's like there's something almost magical. It's a multiplicative effect. For the early primates that evolved this ability, it was a huge advantage, one that would eventually be passed on to us.

And color still plays a huge part in our lives today. Color helps us communicate, attract attention, and even express emotions. We often take it for granted, but it massively enriches our experience of the world. Good boy.

But our focus on vision has come with some trade-offs, namely, our poor sense of smell. Like most humans, I'm experiencing this wonderful vista here with my eyes. But the dog's experiencing this in a very different way. This is a world of smells.

We think that a dog's sense of smell is anywhere from a thousand to a million times better than ours. Like many mammals, it's his main way of understanding the world around him. This fundamental difference in our sense of smell is also reflected in our DNA. A dog has about a thousand genes that are devoted to detecting odors.

We have roughly the same number, but about 600 of them don't work anymore. They're relics. It's a similar story in other primates with color vision.

These broken genes reveal another legacy of our primate past. As our distant ancestors gained this wonderfully rich sense of color vision, what happened was our sense of smell became less important. And in the evolutionary world, it's use it or lose it.

And that's exactly what happened to our sense of smell. It diminished over time. So while we can thank our inner monkey for our wonderful color vision, we can also blame it for our lousy sense of smell. Of course, we humans have also made some radical changes to the ancient primate body plan. Unlike monkeys, we stand up on our own two feet.

You know, animals have been walking on this planet for over 365 million years, and for the most part that walking has been on four legs. Walking on two legs is a fundamentally strange way to get around. No other primate, and very few other mammals move this way. It's a change that had profound effects on the human body. Which begs the question, how on earth did it happen?

The best place in the world to answer this question is in Africa. A site where the Great Rift Valley cuts deep into ancient rocks, exposing fossils from our distant past. These are the remote badlands of northern Ethiopia.

Look at those rocks, they're boom, boom, boom, boom, boom, just totally stretched out. As a paleontologist, that is what I dream about. This is truly in the middle of nothing. Now see the volcanic ash dropping out? That's 3.4 million years old.

That is incredible. My guide is Don Johansen, one of the first people to hunt for fossils here back in the early 70s and a childhood hero of mine. There's the camp.

They're on the far side of the river right there. Two of the most important fossils for understanding the origins of bipedalism have been found in this small region of Ethiopia. Don's taking me to see where the first iconic fossil was found.

A 3.2 million year old human ancestor known as Lucy. It was a Sunday morning back in 1974. So I came up here, looked at this, had no idea what was waiting. It was right in this area, right here. What I saw was a fragment of bone, and I looked at it and almost instantaneously said, that's a hominid.

Wow. Lucy made headlines around the world because although she looked like an ape she walked on two legs she was a biped at that stage the most ancient anyone had found once we broke that three million year barrier it was a whole new picture of what our earliest ancestors looked like the one of the most exciting moments of my my entire career Since dawn first came here in the 70s, scientists have organized expeditions here most years. They found over 400 individual fossils from Lucy's species.

But it's Lucy I most want to meet. Her bones are some of the best evidence we have for what early bipeds looked like. Now of course if this were all articulated properly, you know, with the vertebra on top of it, she'd be about three and a half feet tall. You don't see that.

Yeah, you don't get that. Here's the femur. That's the left. Top end of the thigh bone. And this one also, when you put it all together, now you have...

you know this is telling bipedal this is giving a hint of bipedal this certainly tells it was bipedal that kids in like that which is very characteristic our knees are close together they have to decide chimps come straight up having the upper and lower leg in a straight line is no good for a biped it makes for an awkward waddling game Lucy's legs formed an angle. Her knees were closer together, just like our own knees. This positions the feet directly underneath the body, making walking easier and more efficient.

So Lucy walked much like us. But she wasn't human. She had many primitive features, too.

This is a real mix, you know. This is a real mix. Yeah, it's amazing.

This is very primitive, right? Ape-like. Very small brain. And very ape-like proportions. Bipedal.

Bipedal. Cool. And these hands would have stretched down to about here. So down, yeah, to the neomar. It's just so utterly fabulous.

Isn't it interesting they had the pile of bones, you put her here and all of a sudden you can see that it was a living person. She's beautiful. Yep.

Thank you. We named her after the people and the land. We named her Australopithecus afarensis, from the Afar region. So imagine if Lucy was here with us right now.

What would she look like? Well, she'd be short. She's only about 3 and 1 half feet tall. And the one thing that would be familiar to us, she would be walking upright. With those long, arms reaching almost down to her knees.

She probably had a very odd gait. And as she got closer, we'd see that she had a very ape-like face. I don't think you would see much of a glimpse. of philosophical thought with her eyes. I think in many ways she looked like the ape that stood up.

Yeah. You know? That's amazing. Lucy tells us that by 3.2 million years ago, our ancestors had fully committed to walking on two legs. What she can't tell us is how our ancestors first started walking upright.

To answer that question, we need to meet a second iconic fossil, found just 50 miles from the Lucy site. This fossil, called Ardipithecus, has turned our ideas about how we became bipedal on their head. I've come to Berkeley, California to meet the guy who led the team that discovered ARTIE, an old colleague of mine, Tim White. Tim's out in the field in Ethiopia most years, and he documents his work meticulously with a video camera.

These rarely seen field tapes date from the early 90s. What we wanted to do was to plumb the unknown, to figure out what came before the Lucy species. We just literally didn't know what we would find. Since 1992, the team has run annual expeditions to a remote site called the Middle Awash. Some of the rocks here were millions of years older than the nearby Lucy site.

You see the two resistant bands up there on the hill, they're digging into the lower band. Both of these are dated to 4.4 million. This was really...

We nailed it. So anything between that is 4.4 million years. This band of ancient rock yielded some tantalizing fragments. So they scoured this layer for months on end. The breakthrough finally came in 1994. An Ethiopian graduate student, Yohannes Helisilasi, found a fragment of hand bone in that same layer.

He picked up and said, this looks like a hominid. So we scraped and brushed that surface, and we found some of these hominid hand and foot bones in place. And so we focused on that little hill.

And we turned the video camera on and dug. Oh, wow. This is the way we took it off, virtually a millimeter at a time.

You've got to be really careful. You scratch that, you put your signature on it forever. Here comes the mandible.

Canine's off on the left-hand side right there. Here are the teeth coming out. You know, so as a paleontologist, you're the first people in the entire planet to see that. That's been buried for 4.4 million years.

This was a hugely significant find. A new species of hominid at a critical moment in human evolution. A time when our ancestors were just beginning to walk on two legs.

So while they were still in the field, Tim wanted to collect as much information as he could about Artie's world. What we're out to do is to understand everything we can about that time slice. And at 4.4 million years, anything we learn is new. And so that means bringing in... Sedimentologists who understand what kind of a setting, was it a river, was it a floodplain, bringing in paleontologists expert in the plants, in the birds, in the shrews.

Wherever they found arty species, they found woodland creatures, parrots, monkeys and peacocks, as well as woodland plants. It was a woodland, not an open savanna setting. Now that's a surprise.

These are woodland animals. That runs counter too. So much of what runs canter all the way back to the 1800s For over a hundred years. There's been one main theory of how our ancestors started to walk on two legs The theory goes like this we started out as apes that lived in the trees We looked like chimpanzees and walked on all fours using the knuckles of our hands, but the climate changed And only after Forest had turned to Savannah did we start walking on two legs instead of four. Artie tells a very different story.

She was already walking upright while living in the woodlands. Artie's skeleton ran counter to the old theory too. It was unlike anything anyone had seen before. It took a team of experts 15 years to fully piece her together. So how do we know she was bipedal?

The man in charge of figuring out how Artie might have moved was anatomist Owen Lovejoy. The critical thing in bipedality is the structure of the pelvis. And at first when you look at this bone, you might think that there's not much information here.

But actually there's an enormous amount of information that tells you a great deal about what the original bone looked like. Using information from this deformed bone, the team was able to find out able to reconstruct Artie's entire pelvis. This is a plastic structure that's produced by a three-dimensional printer.

The top part of Artie's pelvis looks more human. The hip bone is short and broad, a key indicator of bipedalism. But the lower half is much longer than a human pelvis, more useful for climbing.

When you got to that detail, you realized it was a mosaic of anatomy that had never been encountered before. It suggests that Artie could walk on two legs, but not as well as later hominids like Lucy. And the rest of her anatomy held surprises too. Neither Lucy nor humans have the ability to grasp with their big toe, but this thing had full grasping ability. So she has a grasping foot that can walk?

Yes. Even the hands were a mosaic. Incredibly long fingers, good for climbing, but a shorter human-like palm.

And the bones show none of the telltale signs that she walked on her knuckles like a chimpanzee. So we now have a detailed picture of the crucial time when our ancestors had just started walking on two legs. Hardy was small, around four feet tall. A good climber, she moved on all fours when in the trees, but she walked upright when on the ground.

She blows the old theory of how we became bipedal out of the water. Not only did our ancestors start walking on two legs when still living in the woods, they never looked or moved like our closest living relative, the chimpanzee. Some scientists don't accept this interpretation.

They think Artie isn't a human ancestor at all, but the relic of an extinct ape. But Tim's spent years studying many specimens of Ardipithecus, and he thinks the evidence is clear. When we looked at the Ardi cranium, we saw very small canines. No other ape, living or fossil, has such reduced canines. That's a good indicator.

She's come in our direction a bit. Go to the pelvis, same thing. A unique adaptation shared by humans and Lucy.

We're still not sure exactly why a woodland climber needed to walk on two legs. But thanks to ARTIE, we now have a snapshot of one of the most dramatic transformations in the history of our species. The transition from walking on four legs to walking on two.

This major change to our ancestral body plan has serious consequences for us today. These consequences can be seen within our own bodies, and they're not all good. This vault in the bowels of the Cleveland Museum of Natural History is the place to go if you want to find out what can go wrong with the human skeleton.

Dr. Bruce Latimer is an anthropologist and anatomist who was a curator here for many years. Well, this is the Hammond-Todd collection, which is the largest collection of its type in the world. There are over 3,000 skeletons in this room.

In each one of these drawers is a complete human skeleton. They come from unclaimed bodies at a Cleveland morgue dating from the early 1900s. If you study these skeletons, one thing becomes clear pretty quickly. The human back goes wrong.

A lot. There's an enormous amount of back problems. The pain must have been phenomenal. And you just see that all over this collection.

Turns out, our bad backs are an unwelcome inheritance from our inner monkey. We took a skeleton like this that was essentially horizontal. We stood it upright. We've had to change essentially every bone to allow us to do that.

And we forced it into this new position. We have a problem going from this kind of animal into that kind of animal, and our main problem is balance. On all fours, the weight of our body hangs down from our spine. But turn this body upright, and the weight is all out front.

It puts us out of whack, totally out of balance. In order to balance, we had to create this curve on your back. And then, your head would be back here, wouldn't it? So we had to create another curve here in the middle of your chest, and then your head would be sticking out in the front, so we had to create another curve in your neck. So we have this S-shaped curve in our spine, and we expect that to hold us up.

That is an engineering nightmare. Our S-shaped spine is unique among mammals, and it causes all sorts of problems. The vertebrae that make up the bones of your back, and the discs between them, are put under a lot of pressure, particularly the ones at the very apex of the biggest curve, the thoracic vertebrae. If you take those thoracic vertebrae and you push on them from the ends too hard, what happens is this. You end up with what's called a wedge fracture.

That curve has crunched it. No other animal has anything even remotely like this. It's a consequence of how we walk. And it's not just fractured vertebrae.

From slip discs to sciatica, our spines go wrong in all kinds of ways. 80% of all Americans will complain of back problems at some point in their lives. Our inner monkey has a lot to answer for.

But I don't want you to get the wrong idea. Standing up on two legs wasn't all bad, or it never would have happened in the first place. It freed our hands, an anatomical change that, combined with our amazing brains, would eventually allow us to make tools and reshape the world around us.

This key moment in our evolutionary history is once again visible in the rocks of northern Ethiopia. So geologically, one of the things that's special about this is it has lots of layers. Lucy's from one part of it, and we're going to another, right?

That's right. We've just jumped about 600,000 or 700,000 years in time. And that is kind of mind-blowing. Yeah. Paleontologist Bill Kimball has brought me to a site where you can find stone tools that are over 2 million years old.

If you know what you're looking for. for so what do I look for well you'll look for flakes on the ground what was that bone that is a piece of fossil bone and here's another one can't find tool like if I'm bone yeah yeah the important thing about tools is it's the hand and the brain right it's it's it's both together absolutely you got one this is very typically nice one I don't get this at all yeah I know it looks like something from your driveway the tool Don's found was made by human ancestors called homo habilis who lived a million years later than lucy clearly some early human took a stone a hammer stone and struck it right there and got oh yeah you got striated field that edge You could use it to strip off meat or whatever. So from this rock you can tell where they hid it, how they hid it.

It's almost like a time machine you have. It is. It's a time machine that takes us back to a period when the faintest glimmers of what it means to be human are beginning to emerge. The use of the hand, the cognition, the repeated behavior to produce a stylized tool. It's mind blowing.

Wow. Can we look for tools? I want to find a tool. No, that's natural. No, this is one.

You found one. Making tools takes excellent vision, fine motor skills, and a brain that can integrate the two. We humans only have this sort of brain because it's been shaped by our ancient primate past.

Monkey, ape, or human, our brains share a basic architecture that's different from most other mammals. We all have a special region involved with hand-eye coordination. And a greatly expanded visual system with as much as 40% of the brain involved in seeing.

Our inner monkey hasn't just shaped our bodies, it's shaped our brains as well. But if you look at the modern world around us, and everything humans have been able to build, from satellites to skyscrapers, there's no doubt we're more intelligent than monkeys. So what changed? What made our brains so different from those of other primates?

Hi, Neil Schuman. Hi, Neil. This is Tom Burbacher.

Welcome to the infant primate lab. So this is the monkey place, huh? This is the monkey place.

Tom Burbacher studies monkeys in order to answer questions about our own brains. He's going to show me an experiment that demonstrates an important difference between our brains and the brains of a monkey. But the differences aren't what you might expect, especially when we're young. Monkey on the set.

Monkey on the set. Neil, this is CI. She's a three-month-old pigtail macaque.

This experiment tests something called object permanence. In other words, whether this monkey knows an object still exists when she can't see it. It's a developmental milestone for both monkeys and humans.

You're going to put a piece of fruit on the toy itself. You'll place it in the well. She's looking at it.

There. And you'll move that to completely hide that toy. Okay.

There you go. Wow! There you go.

Wow! That is impressive. Object permanence. Boom, boom. Three months old, and already CI understands object permanence.

CI, you are good. Hi Geneva, how are you? You are a cutie. Geneva is the same age as the baby monkey. I'm going to do the exact same test on her under the expert eye of child development specialist, Professor Susan Speaker.

She needs to reach for him, show that she's interested. Oh, I think we got interest. She's got a good reach.

You do, look at you. Oh, Geneva, you like those. Hello! Now, Neil, can you get them away?

Oh, I'm an expert at this. Can I take that for a sec? Sorry, it's temporary. You are so good that way.

I'll pop it in. Make sure she's watching. She's watching.

We'll cover it up, watch this. And she wonders, what did you do, Neil? What toys?

I don't know where they went. Wow, that is amazing. Where did they go? It is incredible. If it's not there, it doesn't exist.

Right. That is amazing. So how come a baby monkey beats a baby human in this test?

These tests are showing us how rapidly a particular region of our brain is wiring up in development. And it's showing us comparatively that we wire up much slower in this part of the brain than do monkeys. Compared to other primates, we humans have an unusually long childhood, even if you take the different lifespans into account.

This should be an evolutionary disadvantage. But in fact, it's one of our greatest strengths. During childhood, our brains are being shaped by our environment and by our experience. Extending this phase gives us longer to learn and pick up new skills. Some think that this is a key part of what makes us so smart.

But there are other factors too. The brain is made up of vast networks of nerve cells called neurons that carry, process, and store information. The part of the human brain responsible for higher thought, the cortex, contains more neurons than that of any other animal on the planet.

An astonishing 16 billion. These neurons are organized in a uniquely powerful way. They're unusually interconnected.

This means we can do things that other primates can't. Build complex tools, compose symphonies, and even investigate how our own brains work. But before we get too carried away with our own cleverness, I want to inject a bit of humility.

That means leaving monkeys behind and going back to where the series began. My anatomy lab in Chicago and my favorite subject, fish. The brain of a fish and the brain of a human have more in common than you might think.

This is a trip to the beginning. This is as basic as it gets. We're going human fish represented by a cartilaginous fish, a shark on the right.

And what you have is you see the muscles and nerves and organs inside the shark head. But importantly you see this yellow tissue. This is the front end of the of the spinal cord.

It's the brain. Doesn't look like much but it's the shark brain. This is the human brain.

This is where it all happens for us. Where our memories reside. Where our, you know, our fears, our loves, our hates.

It's all in here. The human brain, really, at the surface level, looks nothing like what's sitting inside the shark head. Yet when you know how to look, you find a very... profound similarity and that similarity lies in the overall architecture of the brain itself in the human we have a forebrain and that forebrain consists of this folded tissue here or much of our conscious thought happens and then there's a midbrain this walnut sized area in the middle And then a hindbrain.

That's a fundamental division. We see that in development, and we see that based on where the nerves exit the brain. Well, if you follow the similar nerves in a shark, what you see is sharks, too, have that same structure.

A forebrain, a midbrain, and a hindbrain. There's a fundamental architectural similarity among all brains. The brains of people, the brains of dogs, the brains of cats, the brains of monkeys, lizards, frogs, salamanders, trout, bass, even sharks and fish are similar. Each one of them has a forebrain and a midbrain and a hindbrain, despite the fact that those brains are often very different in function and form. But that's not the end of the story.

The fundamental architecture of our own brains can be traced back even further than fish, to a surprisingly primitive animal that doesn't even really have a brain. But I've got to find these tiny creatures. first. All right, OK.

Well, we could start trying around here. Thanks, Master Spock. Thanks, Master Spock. Let's give it a go.

This is Peter Holland, a world-renowned geneticist and head of zoology at Oxford University in England. Okay, so what do I do? Just shake it.

Shake and bake, huh? I'll make it look so easy. That?

No. That'll be pretty obvious because they'll really swim around. The water makes the digging slightly harder. It does.

You got one. There's an amphioxid. We got any?

Whoa, look at that little guy go. Hey! Just dip it in the water again, you'll see it. Well, they really flick.

There he is. Hey, that's beautiful. Look at that.

Which is the front? It doesn't look like much, but this tiny creature called amphioxus has much to tell us about our own brains. That is cool.

Okay, that ranks as cool. Okay, so let's take a look at a couple of these. So I brought this from the anatomy lab in Chicago. This is a human brain. When I look at this, I don't find any obvious similarities to that.

Deep in the genes of this animal and the development of this animal and deep in the genes of us and the development of us, there are the similarities. They're pretty active. Holy cow.

Oh, that is beautiful. God, they're so clear, too. You can see right through them. That's amazing.

Amphioxus lives in the sand of the ocean floor, filtering algae out of the water. It's from an incredibly ancient group of animals. We found fossils that look a lot like... This and rocks that are over 500 million years old.

They are a window into what came before the first fish. And crucially, they don't have anything like what we'd call a brain. The simple nerve cord that runs the length of their body ends with just a tiny swelling invisible to the naked eye.

If you look at the front end of this animal, you don't see it all expanded into a large skull or brain region. It's just pointed. But if you look at the genetic makeup of these ancient creatures, you find something truly remarkable.

To make the forebrain, midbrain, and hindbrain that we saw in our lab, you need a series of control genes to tell the cells within the developing brain where they are. They're like a zip code. Those same control genes that make our own brains are active in Amphioxus. But here, they're simply building the primitive nerve cord and the tiny swelling at its front. This means that the genetic roots of our complex primate brains existed in much simpler creatures that first arose over 500 million years ago.

I think it gives us a glimpse into where our brains came from. Into the basic organization of the brain of our ancestors. I mean, I find that mind-blowing.

He's just an exciting animal. He knows you're talking about him. See, he's going.

That's right. He's going. You can see that. muscle blocks really working that um yeah and i think to an evolutionary but well he's oh sorry he's going uh tectonic on this he's going land living uh he's got a road yeah he's gone for the next transition exactly he's in the devonian now The search for our inner fish has taken me from high in the Arctic Here was the snout of exactly the creature we were looking for to the plains of Africa Yeah, I just want to run down here and start collecting fossils Let's go as well as deep inside our own DNA And today we saw a little tiny worm living in the mud here in the bay that contains genes that we have that sculpt our own brains. The organ that gives us many of our unique properties.

We've seen how our distant relatives, from worms to fish, from reptiles to early primates, have defined our bodies. At each new stage of our journey along the tree of life, our ancient animal ancestors have reconfigured what's gone before. And that's how we ended up as the intelligent creatures with all our quirky flaws that dominate the planet today. There's something incredibly profound, and I think beautiful, in the idea that inside every organ, cell, and gene of our body lie deep connections to the rest of life on our planet.

Transcript for:The Evolution of Human Anatomy

Transcript for:
The Evolution of Human Anatomy