[MUSIC] So welcome back. Some of the most divergent genes between us and chimps are involved with such traits as burn surface proteins, probably to do with the chimps being polygamous philanderers, whereas we are more monogamous. There are also a lot of differences between us and chimps in how we regulate gene receptors for hormones made of peptides. Peptides are chains of amino acids considered too small to be called proteins. Examples include oxytocin and vasopressin. These are hormones involved in social interactions and bonding, and I'll be discussing them in later lectures. Oxytocin is often called the cuddle hormone, and vasopressin in us, is said to be involved in pair bonding. But, we're just beginning to understand how these hormones do what they do. Now, the human mating system is unique among apes, in that males and females pair bond and share child rearing. That leads to a whole set of tendencies untypical of apes, such as the preference of men for youthful looking mates and the preference of women for high status, often older men. The idea is that a male wants to bond with a young mate because she would have more years of child bearing, while a woman wants a high status male because he'll be better able to provide food and protection. Now if you're a man, you may think it is natural to like younger women, but you're taking your preferences for granted. In chimps, and presumably therefore, our ancestors before we took up monogamy, older is sexier than younger. A male chimp would jump right over a young female to get to a old experienced one because whoever the mother is, she'll have to bring up the big baby without his help. She can have sole responsibility for bringing up baby, and a experienced mother is gonna be better able to do that than a young one. So now just because we've been focusing on the human genome, I don't want you to get the idea that the chimp is somehow a failed design. A chimp is very good and well designed at being a chimp. Chimps are not halfway to being human, they're not failed humans. Chimps evolved to be able to swing through the trees. Its direction of evolution is, therefore, different than ours. A chimp is a perfectly adapted at being a chimp. There's evidence from genomics, as well as their bone structure, that chimps have changed, at least as much from our putative last common ancestor, as we have. Now do you remember I said that was more bipedal than the chimp? So chimp genes change rapid evolution include many for the musculoskeletal system. It's given in their incredibly powerful arms and their great massive chests so they can swing through the trees. Other rapidly evolving chimp genes include many encoding components of white blood cells, add immunity. A lot of scientists are interested in, why are chimps better protected than us against many diseases? Chimps don't get HIV, hepatitis, asthma, acne, and many cancers. Would you object to some genetic engineering of our DNA if it gave us the same protection chimps have? Cancer kills one in four of us. Don't do that to to chimps. On a later lecture, I'll explain that some of the reasons chimps get less cancer may be related to a process called epigenetics. And we're going to have a look at the incredibly exciting field of paleogenomics. Paleontology used to land the appearance of fossils to deduce our history. But now the Max Planck Institute, in particular, developed techniques to extract little bits of DNA from little fragments of bone and get a whole lot of sequence data. This sort of technology means we can mine the wealth of fossil material out there and study evolution in real time. A lot of stuff we had thought impossible is now possible. In particular, we're able to answer questions about human evolution and history that would have been unapproachable, just a few years ago. So the Max Planck Institute took most of their original genomic sequence from three small pieces of Neanderthal bone. And in 2013, a better quality Neanderthal genome came from a toe bone. A tiny bone fragment from a little pinky finger at the Denisova Cave site in Siberia identified a new distant cousin of ours, a rather closer relation than Neanderthals that lived 40,000 years ago. These five pieces of bone have provided the most information we've ever gotten from the fossil record. Let's have a quick big picture overview of our evolution. I think it here shows Christopher Stringers' hypothesis of the family tree of genus Homo published in 2012. You may remember that I mentioned Homo erectus, the key species that came far. Well, he originated in Africa about 2 million years ago. Soon after it emerged from Africa, it gave rise to people in China, Java, and so on. This Homo erectus skull, here, was modeled from one found in China. It's very famous. He had a brain size of about 900 cubic centimeters, compared to ours of about 1,350. Now, okay, about 800,000 years ago, Homo erectus gave life to a new species, Homo heidelbergensis. And that species then split to become us and Neanderthals. Basically, north of the Mediterranean, it evolved into Neanderthals, and south of the Mediterranean, in Africa, it gave rise to us. Well, we always knew it was going to more complex than that. There was the strange hominid known as Homo floresiensis that lived on the islands of Florence until just 12,000 years ago. They've been nicknamed the hobbits because they were small. But they had big feet. Some suggest that these little hobbits may have been a dwarf version of Homo erectus. Then there's also a number of fossils in China and India that have been very hard to place. However, thanks to genomic sequence data we now know that in its eastern range, Heidelbergensis evolved into another species that we call Denisovans. We don't have a Denisovan skull so we don't know what they looked like, but we do have a lot of Heidelbergensis skeletons. This is a reconstruction of a Homo heidelbergensis, our last common ancestor with Neanderthals and Denisovans. He was a very big, muscular fellow. It had a short stabbing spear. It was an apex predator, that means it was on top of the food chain. And we know that because Heidelbergensis took his time and methodically carved up his large prey. It didn't fear lions or tigers. And it was smart, it had a typical cranial capacity of 1,100 to 1,400 cubic centimeters, which overlaps our 1,350 CC average. We actually have a smaller brain than Neanderthals, again on average. And you can see from the family tree that Neanderthals represent the last divergent branch of the human evolutionary bush. So big picture stuff, why do we want the Neanderthal genome? When we compare ourselves with chimps, a lot of the mutations would have happened a long time ago in our lineage, in our family tree. We're looking at ancient mutations that happened millions of years ago in Australopithecines, in Homo habilis, in Homo erectus, and Homo heidelbergensis. By comparing the human and Neanderthal genomes, we can identify sequences which changed recently, in the last few hundred thousand years. The finishing genetic touches that made modern humans really human and perhaps gave us an edge. So comparing the genomes may identify inherent genetic differences that allowed us to be the world conquerors. While the poor old Neanderthals, they died out 25,000 years ago. So line the human and Neanderthal genomes up, and you find they're 99.5% identical. You and I are probably 99.9% identical. Neanderthals were lactose intolerant, so they weren't drinking milk. They lacked penile spines which probably helped out with sex between us, and they had red hair and pale skin. We know about the red hair, because the melanocortin receptor that controls the switch between production of red and black pigments, is mutated in Neanderthals. However, it's a mutation not seen in modern humans. When the Neanderthals gene was resurrected in modern human cells, in a laboratory experiment, this mutation impaired receptor activity, a condition that leads to red hair and pale skin in modern humans. Neanderthals and modern humans are on different evolutionary paths to the same red headed appearance. There must be something about living in Europe that leads to mutated skin and hair color because normal human hair color is black. An important aspect that makes us humans is language. Could Neanderthals speak? Well we can look at the changes FOXP2 gene that occurred in the divergence of humans from chimps, and it's clear that Neanderthals had those changes. So, presumably, did our last common ancestor, Heidelbergensis. The elusive Denisovans also had the same sequence, suggesting all four varieties of humans had speech of some kind and an instinct for grammar. Well, perhaps that should make you think about, how would we treat them if they were alive today? Well, there's a big part, we are the same as Neanderthals. So there must be differences in the genomes that tell us how we're different mentally, and certainly physically from Neanderthals and Denisovans. Before genomes, all scientists had to go on was the fossilized bones. Now have a look at this Neanderthal skull. It's clearly quite different than ours. It's got this very low forehead. It's got this long, sloping brain case. It's got this protruding central face here. It's got these very heavy brow ridges. So oblong cranium means their brains were a different shape than ours. At some point, they think their brains may have been anatomically different, so organized different. Obviously, nobody fully knows how Neanderthal brains worked, of how their thinking was different from us. But the genomes have already shown more potential for finding out than the skulls ever did. It turns out that we have eight key gene variants not shared with Neanderthals and Denisovans that would allow neurons to project further across the brain and connect with one another. They may have allowed our direct ancestors' brains to become more complex. But interestingly changes in these genes in us are also linked with autism and schizophrenia. Now that doesn't necessarily mean Neanderthals and Denisovans had autism-like traits, or conversely, that's we're more prone to autism. Because as we shall see, neurological additions are complex and involve many genes. And afterall, our extinct relatives, the Neanderthals, Fed well for tens of thousands of years. But these aren't genes that affect how we see ourselves, how we put ourselves in the shoes of others, how we manipulate others, how we lie, how we develop politics and To scientists. So these differences in genes for cognitive development likely mean big Neanderthal and Denisovan brains evolved in different societies and to solve different sorts of problems from our big African brains. Well, except they've made some surprisingly beautiful jewelry we know almost nothing about Denisovan culture. But we do know there were big differences between, most of us and most Neanderthals in way of life because Neanderthals seemed to have been high risk, highly cooperative hunters a bit l ike wolves. Like our ancestor heidelbergensis, they had these short stabbing spears showed by the determined looking Neanderthal woman here in this reconstruction. These spears meant they had to be close in to make a kill. Well, anatomically modern humans in Africa, they have their projectile weapons, throwing weapons. It has been suggested that Neanderthals facing high risks as ambush hunters of very big game might've benefited from an ability to imagine and anticipate the reactions of their prey. Perhaps that's what some of the genetic differences are about. Now of course we're principally interested in comparing what we can of our cognitive abilities with Neanderthals, but their bodies were also quite distinctive. Look at this sample Neanderthal skeleton. It makes clear that their very large bell like chest cavity, and their very wide pelvis, at least in comparison with us Their bodies were also very compact in shape. They effectively had no waist. Possibly it's adjusted as an adaptation against the cold. Now the RUNX2 sequence in Neanderthals is different than ours. Which is particularly fascinating, because when mutated in humans it can lead to skeletal problems that in some aspects mimic the differences in neanderthals and humans. And can lead to one of us, having a great big bell shaped rib cage, similar to neanderthals. So we are getting to know enough about our genomes to predict how differences from Neanderthals account for them not being the same as us. RUNX2 is a master regulator that activates a network of genes involved in their formation. It's just another example of how a changing a minute portion of our genome can profoundly affect our biology. [BLANK AUDIO] [CHIMP NOISES]
