By understanding more about these prehistoric people, we can learn about who we are as a species today. Our ancestors' experiences shaped us, and they may still hold answers to some of our current health problems, from diabetes to depression.
Neanderthals were thriving from Siberia to southern Spain by the time a few families of modern humans made it out of Africa around 60,000 years ago. These Africans encountered Neanderthals and, on several occasions, had children with them. We know this because human DNA has been found in the genomes of Neanderthals, and because everyone alive today of European descent—including me—has some Neanderthal DNA in their genetic makeup. Could it be that their genes, adapted to the northerly environment, provided a selective advantage to our ancestors as well?After driving through narrow tunnels on a road that skirts the cliff face, we pull up at a military checkpoint. Clive shows the guard our accreditation and we're waved through to park inside. Safety helmets on to protect from rockslides, we leave the car and continue on foot under a low rock arch. A series of metal steps leads steeply down the cliff to a narrow shingle beach, about 200 feet below. The tide is lapping the pebbles and our feet must negotiate the unstable larger rocks to find a dry path. I've been concentrating so hard on keeping my footing that it is something of a shock to look up and suddenly face a gaping absence in the rock wall. We have reached Gorham's Cave, a great teardrop-shaped cavern that disappears into the white cliff face and, upon entering, seems to grow in height and space. This vast, cathedral-like structure, with a roof that soars high into the interior, was used by Neanderthals for tens of thousands of years. Scientists believe it was their last refuge. When Neanderthals disappeared from here, some 32,000 years ago, we became the sole inheritors of our continent.
Between one and four percent of our DNA is of Neanderthal origins.
These people evolved outside of Africa but clearly had advanced culture and the capability to survive in a hostile environment. "Consider modern humans were in the Middle East perhaps 70,000 years ago, and reached Australia more than 50,000 years ago," says Clive. "Why did it take them so much longer to reach Europe? I think it was because Neanderthals were doing very well and keeping modern humans out." But by 39,000 years ago, Neanderthals were struggling. Genetically they had low diversity because of inbreeding and they were reduced to very low numbers, partly because an extreme and rapid change of climate was pushing them out of many of their former habitats. A lot of the forested areas they depended on were disappearing and, while they were intelligent enough to adapt their tools and technology, their bodies were unable to adapt to the hunting techniques required for the new climate and landscapes. "In parts of Europe, the landscape changed in a generation from thick forest to a plain without a single tree," Clive says. "Our ancestors, who were used to hunting in bigger groups on the plains, could adapt easily: Instead of wildebeest they had reindeer, but effectively the way of capturing them was the same. But Neanderthals were forest people. "It could've gone the other way—if instead the climate had got wetter and warmer, we might be Neanderthals today discussing the demise of modern humans." Although the Neanderthals, like the Denisovans and other races we are yet to identify, died out, their genetic legacy lives on in people of European and Asian descent. Between 1 and 4 percent of our DNA is of Neanderthal origins, but we don't all carry the same genes, so across the population around 20 percent of the Neanderthal genome is still being passed on. That's an extraordinary amount, leading researchers to suspect that Neanderthal genes must be advantageous for survival in Europe. Interbreeding across different races of human would have helped accelerate the accumulation of useful genes for the environment, a process that would have taken much longer to occur through evolution by natural selection. Neanderthal tweaks to our immune system, for example, may have boosted our survival in new lands, just as we prime our immune system with travel vaccines today. Many of the genes are associated with keratin, the protein in skin and hair, including some that are linked to corns and others that play a role in pigmentation—Neanderthals were redheads, apparently. Perhaps these visible variants were considered appealing by our ancestors and sexually selected for, or perhaps a tougher skin offered some advantage in the colder, darker European environment. Some Neanderthal genes, however, appear to be a disadvantage, for instance making us more prone to diseases like Crohn's, urinary tract disorders, and type 2 diabetes, and to depression. Others change the way we metabolize fats, risking obesity, or even make us more likely to become addicted to smoking. None of these genes are a direct cause of these complicated conditions, but they are contributory risk factors, so how did they survive selection for a thousand generations? It's likely that for much of the time since our sexual encounters with Neanderthals, these genes were useful. When we lived as hunter-gatherers, for example, or early farmers, we would have faced times of near starvation interspersed with periods of gorging. Genes that now pose a risk of diabetes may have helped us to cope with starvation, but our new lifestyles of continual gorging on plentiful, high-calorie food now reveal harmful side-effects. Perhaps it is because of such latent disadvantages that Neanderthal DNA is very slowly now being deselected from the human genome. While I can (sort of) blame my Neanderthal ancestry for everything from mood disorders to being greedy, another archaic human race passed on genes that help modern Melanesians, such as people in Papua New Guinea, survive different conditions. Around the time that the ancestors of modern Europeans and Asians were getting friendly with Neanderthals, the ancestors of Melanesians were having sex with Denisovans, about whom we know very little. Their surviving genes, however, may help modern-day Melanesians to live at altitude by changing the way their bodies react to low levels of oxygen. Some geneticists suspect that other, yet-to-be-discovered archaic races may have influenced the genes of other human populations across the world.
Interbreeding with Neanderthal and other archaic humans certainly changed our genes, but the story doesn't end there. I am a Londoner, but I'm a little darker than many Englishwomen because my father is originally from Eastern Europe. We are attuned to such slight differences in skin color, face shape, hair, and a host of other less obvious features encountered across different parts of the world. However, there has been no interbreeding with other human races for at least 32,000 years. Even though I look very different from a Han Chinese or Bantu person, we are actually remarkably similar genetically. There is far less genetic difference between any two humans than there is between two chimpanzees, for example.
The reason for our similarity is the population bottlenecks we faced as a species, during which our numbers dropped as low as a few hundred families and we came close to extinction. As a result, we are too homogeneous to have separated into different races. Nevertheless, variety has emerged through populations being separated geographically—and culturally, in some cases—over thousands of years. The greatest distinctions occur in isolated populations where small genetic and cultural changes become exaggerated, and there have been many of them over the 50,000 years since my ancestors made the journey out of Africa towards Europe. According to the analysis of my genome, my haplogroup is H4a. Haplogroups describe the mutations on our mitochondrial DNA, passed down through the maternal line, and can theoretically be used to trace a migratory path all the way back to Africa. H4a is a group shared by people in Europe, unsurprisingly, and western Asia. It is, the genome-testing company assures me, the same as Warren Buffet's. So what journey did my ancestors take that would result in these mutations and give me typically European features?"I was dumped by helicopter in the wilderness with two other people, a Russian and an indigenous Yukaghir man, with our dogs, our guns, our traps, a little food, and a little tea. There we had to survive and get food and furs in the coldest place on Earth where humans live naturally—minus 60 degrees." Eske Willerslev lived for six months as a trapper in Siberia in his 20s. Separately, his identical twin brother Rane did the same. When they were teenagers, their father had regularly left them in Lapland to survive alone in the wilderness for a couple of weeks, fostering a passion for the remote tundra and the people who live there, and they went on increasingly lengthy expeditions. But surviving practically alone was very different. "It was a childhood dream, but it was the toughest thing I have ever done," Eske admits. These experiences affected the twins deeply, and both have been driven towards a deeper understanding of how the challenge of survival has forged us as humans over the past 50,000 years. It led Eske into the science of genetics, and to pioneering the new field of ancient DNA sequencing. Now director of the Centre for GeoGenetics at the Natural History Museum of Denmark, Eske has sequenced the world's oldest genome (a 700,000-year-old horse) and was the first to sequence the genome of an ancient human, a 4,000-year-old Saqqaq man from Greenland. Since then, he has gone on to sequence yet more ancient humans and, in doing so, has fundamentally changed our understanding of early human migration through Europe and beyond. If anyone can unpick my origins, it is surely Eske. First, though, I go to meet his twin Rane, who studied humanities, went into cultural anthropology and is now a professor at Aarhus University. He's not convinced that his brother's genetic approach can reveal all the answers to my questions: "There exists an uneasy relationship between biology and culture," he tells me. "Natural scientists claim they can reveal what sort of people moved around, and they are not interested in having their models challenged. But this cannot tell you anything about what people thought or what their culture was." To put this point to Eske, I visit him in his delightful museum office, opposite a petite moated castle and in the grounds of the botanic gardens—there could scarcely be a more idyllic place for a scientist to work. Greeting him for the first time, just hours after meeting Rane, is disconcerting. Identical twins are genetically and physically almost exactly the same – looking back, many years from now, at DNA left by the brothers, it would be all but impossible to tell them apart or even to realize that there were two of them. Eske tells me that he is increasingly working with archaeologists to gain additional cultural perspective, but that genetic analysis can answer questions that nothing else can. "You find cultural objects in certain places and the fundamental question is: Does that mean people who made it were actually there or that it was traded? And, if you find very similar cultural objects, does that mean there was parallel or convergent cultural evolution in the two places, or does that mean there was contact?" he explains. "For example, one theory says the very first people crossing into the Americas were not Native Americans but Europeans crossing the Atlantic, because the stone tools thousands of years ago in America are similar to stone tools in Europe at the same time. Only when we did the genetic testing could we see it was convergent evolution, because the guys carrying and using those tools have nothing to do with Europeans. They were Native Americans. So the genetics, in terms of migrations, is by far the most powerful tool we have available now to determine: Was it people moving around or was it culture moving around? And this is really fundamental."
The things that we thought we understood about Europeans are coming unstuck as we examine the genes of more ancient people.