It's a fact of the archaeological record: Modern humans survived and Neanderthals did not. Why? And what does it teach us about our own survival?
Neanderthals were humans who went extinct between 20,000 and 30,000 years ago. Though there is some debate about who these people were, there is no question that there are none left. All that remains of the hundreds of Neanderthal groups that roved across Europe and Central Asia are a handful of ambiguous funeral sites, bones, tools, and pieces of art-along with some DNA that modern humans inherited from them. How can we avoid meeting the Neanderthals' fate? That depends on what you think wiped out these early humans in the millennia after they met H. sapiens.
By 40,000 years ago, humans had spread in waves across most of the world, from Africa to Europe, Asia, and even Australia. But these humans were not all perfectly alike. When some groups of H. sapiens poured out of Africa, they walked north, then west. In this thickly forested land, they came face-to-face with other humans, stockier and lighter skinned than themselves, who had been living for thousands of years in the cold wilds of Europe, Russia, and Central Asia. Today we call these humans Neanderthals, a name derived from the Neander Valley caves in Germany where the first Neanderthal skull was identified in the nineteenth century.
Neanderthals were not one unified group. They had spread far enough across Europe, Asia, and the Middle East that they formed regional groups, something like modern human tribes or races, who probably looked fairly different from each other. Neanderthals used tools and fire, just as H. sapiens did, and the different Neanderthal groups probably had a variety of languages and cultural traditions. But in many ways they were dramatically unlike H. sapiens, leading isolated lives in small bands of 10 to 15 people, with few resources. They had several tools, including spears for hunting and sharpened flints for scraping hides, cutting meat, and cracking bones. Unlike H. sapiens, who ate a wide range of vegetables and meat, Neanderthals were mostly meat-eaters who endured often horrifically difficult seasons with very little food. Still, there is evidence that they cared for each other through hardship: fossils retrieved from a cave in Iraq include the skeleton of a Neanderthal who had been terribly injured, with a smashed eye socket and severed arm, whose bones had nevertheless healed over time. Like humans today, these hominins nursed each other back to health after life-threatening injuries.
Roughly 10,000 years after their first meeting with H. sapiens, all the Neanderthal groups were extinct and H. sapiens was the dominant hominin on Earth. What happened during those millennia when H. sapiens lived alongside creatures who must have looked to them like humanoid aliens?
A few decades ago, most scientists would have answered that it was a nightmare. Stanford's Richard Klein, who spent years in France comparing the tools of Neanderthals and early H. sapiens, lowered his voice a register when I recently asked him to describe the meeting between these hominin groups. "You don't like to think about a holocaust, but it's quite possible," he said. He referred to the long-standing belief among many anthropologists that H. sapiens exterminated Neanderthals with superior weapons and intellect. For a long time, there seemed to be no other explanation for the rapid disappearance of Neanderthals after H. sapiens arrived in their territories.
Today, however, there is a growing body of evidence from the field of population genetics that tells a very different story about what happened when the two groups of early humans lived together, sharing the same caves and hearths. Anthropologists like Milford Wolpoff, of the University of Michigan, and John Hawks have suggested that the two groups formed a new, hybrid human culture. Instead of exterminating Neanderthals, their theory goes, H. sapiens had children with them until Neanderthals' genetic uniqueness slowly dissolved into H. sapiens over the generations. This idea is supported by compelling evidence that modern humans carry Neanderthal genes in our DNA.
Regardless of whether H. sapiens murdered or married the Neanderthals they met in the frozen forests of Europe and Russia, the fact remains that our barrel-chested cousins no longer walk among us. They are a group of humans who went extinct. The story of how that happened is as much about survival as it is about destruction.
The Neanderthal Way of Life
We have only fragmentary evidence of what Neanderthal life was like before the arrival of H. sapiens. Though they would have looked different from H. sapiens, they were not another species. Some anthropologists call Neanderthals a "subspecies" to indicate their evolutionary divergence from us, but there is strong evidence that Neanderthals could and did interbreed with H. sapiens. Contrary to popular belief, Neanderthals probably weren't swarthy; it's likely that these early humans were pale-skinned, possibly with red hair. We know that they used their spears to hunt mammoths and other big game. Many Neanderthal skeletons are distorted by broken bones that healed, often crookedly; this suggests that they killed game in close combat with it, sustaining many injuries in the process. They struggled with dramatic climate changes too. The European and Asian climates swung between little ice ages and warmer periods during the height of Neanderthal life, and these temperature changes would have constantly pushed the Neanderthals out of familiar hunting grounds. Many of them took shelter from the weather in roomy caves overlooking forested valleys or coastal cliffs.
Though their range extended from Western Europe to Central Asia, the Neanderthal population was probably quite small-a generous estimate would put it at 100,000 individuals total at its apex, and many scientists believe it could have been under 10,000. By examining the growth of enamel on Neanderthal teeth, anthropologists have determined that many suffered periods of extreme hunger while they were young. This problem may have been exacerbated by their meat-heavy diets. When mammoth hunting didn't go well, or a particularly cold season left their favored game skinny or sick, the Neanderthals would have gone through months of malnutrition. Though Neanderthals buried their dead, made tools, and (at least in one case) built houses out of mammoth bones, we have no traditional evidence that they had language or culture as we know them. Usually such evidence comes in the form of art or symbolic items left behind. Neanderthals did make art and complex tools after meeting H. sapiens, but we have yet to find any art that is unambiguously Neanderthal in origin.
Still, there are intriguing hints. A 60,000-year-old Neanderthal grave recently discovered in Spain suggests that Neanderthals may have had symbolic communication before H. sapiens arrived. Researchers discovered the remains of three Neanderthals who appeared to have been gently laid in identical positions, their arms raised over their heads, then covered in rocks. The severed paws of a panther were found with the bodies, heightening the impression that the discovery represented a funeral ritual complete with "burial goods," or symbolic items placed in the graves. Erik Trinkhaus, an anthropologist at Washington University in St. Louis, says this site shows that Neanderthals might have had symbolic intelligence like modern humans.
Gravesites like these have led many scientists, including Trinkhaus, to believe that Neanderthals talked or even sang. But we haven't found enough archaeological evidence to sway the entire scientific community one way or the other.
By contrast, the H. sapiens groups who lived at the time of first contact with Neanderthals left behind ample evidence of symbolic thought. Bone needles attest to the fact that H. sapiens sewed clothing, and pierced shells suggest jewelry. There are even traces of red-ochre mixtures found in many H. sapiens campsites, which could have been used for anything from paint or dye to makeup. Added together, these bits of evidence suggest that H. sapiens groups weren't just using tools for survival; they were using them for adornment. And culture as we know it probably started with those simple adornments.
Looked at from the perspective of Neanderthals, then, there might have been a vast gulf between themselves and the newly arrived H. sapiens. The newcomers not only looked different-they were taller, slimmer, and had smaller skulls-but they probably chattered in an incomprehensibly complex language and wore bizarre garments. Would Neanderthals have tried to communicate with these people, or invited them to a dinner of mammoth meat?
There was a lot more than hanky-panky going on.For anthropologists like Klein, who spoke about a Neanderthal holocaust, the answer is an emphatic no. He's part of a school of anthropological thought that holds that H. sapiens would have met the Neanderthals with nothing but hate, disgust, and indifference to their plight. After those Neanderthals watched H. sapiens arrive, the next chapter in their lives would have been marked by bloodshed and starvation as H. sapiens murdered and outhunted them with their superior weaponry. Neanderthals were so poor, and had such a small population, that their extinction was inevitable.
This story might sound familiar to anyone versed in the colonial history of the Americas. It's as if H. sapiens is playing the role of Europeans arriving in their ships, and Neanderthals are playing that of the soon-to-be-exterminated natives. But Klein sees a sharp contrast between Neanderthals and the natives that Europeans met in America. When H. sapiens arrived, he asserted, "there was no cultural exchange" because the Neanderthals had no culture. Imagine what might have happened if the Spanish had arrived in the Americas, but the locals had no wealth, science, sprawling cities, nor vast farms. The Neanderthals had nothing to trade with H. sapiens, and so the newcomers saw them as animals.
Neanderthals may have had fleeting sexual relationships with H. sapiens here and there, admitted Klein, but "modern human males will mate with anything." Tattersall agreed. "Maybe there was some Pleistocene hanky-panky," he joked. But it wasn't a sign of cultural bonding. For anthropologists like Klein and Tattersall, any noncombative relationships forged between the two human groups were more like fraternization than fraternity.
But there is a counter-narrative told by a new generation of anthropologists. Bolstered by genetic discoveries that have revealed traces of Neanderthal genes in the modern human genome, these scientists argue that there was a lot more than hanky-panky going on. Indeed, there is evidence that the arrival of H. sapiens may have dramatically transformed the impoverished Neanderthal culture. Some Neanderthal cave sites hold a mixture of traditional Neanderthal tools and H. sapiens tools. It's hard to say whether these remains demonstrate an evolving hybrid culture, or if H. sapiens simply took over Neanderthal caves and began leaving their garbage in the same pits that the Neanderthals once used. Still, many caves that housed Neanderthals shortly before the group went extinct are full of ornaments, tools, and even paints. Were they emulating their H. sapiens counterparts? Had they become part of an early human melting pot, engaging in the very cultural exchange that Klein and Tattersall have dismissed?
Extermination and Assimilation
The complicated debate over what happened to Neanderthals can be boiled down to two dominant theories: Either H. sapiens destroyed the other humans, or joined up with them.
The "African replacement" theory, sometimes called the recent African origins theory, holds that H. sapiens charged out of Africa and crushed H. neanderthalensis underfoot. This fits with Klein's account of a Neanderthal holocaust. Basically, H. sapiens groups replaced their distant cousins, probably by making war on them and taking over their territories. This theory is simple, and has the virtue of matching the archaeological evidence we find in caves where Neanderthal remains are below those of H. sapiens, as if modern humans pushed their Neanderthal counterparts out into the cold to die.
In the late 1980s, a University of Hawaii biochemist named Rebecca Cann and her colleagues found a way to support the African replacement theory with genetic evidence, too. Cann's team published the results of an exhaustive study of mitochondrial DNA, small bits of genetic material that pass unchanged from mothers to children. They discovered that all humans on Earth could trace their genetic ancestry back to a single H. sapiens woman from Africa, nicknamed Mitochondrial Eve. If all of us can trace our roots back to one African woman, then how could we be the products of crossbreeding? We must have rolled triumphantly over the Neanderthals, spreading Mitochondrial Eve's DNA everywhere we went. But mitochondrial DNA offers us only a small part of the genetic picture. When scientists sequenced the full genomes of Neanderthals, they discovered several DNA sequences shared by modern humans and their Neanderthal cousins.
Besides, how likely is it that a group of H. sapiens nomads would attack a community of Neanderthals? These were explorers, after all, probably carrying their lives on their backs. Neanderthals may not have had a lot of tools, but they did have deadly spears they used to bring down mammoths. They had fire. Even with H. sapiens' greater numbers, would these interlopers have had the resources to mount a civilization-erasing attack? Rather than starting a resource-intensive war against their neighbors, many H. sapiens could have opted to trade with the odd-looking locals, and eventually move in next to them. Over time, through trade (and, yes, the occasional battle) the two groups would have shared so much culturally and genetically that it would become impossible to tell them apart.
This is precisely the kind of thinking that animates what's called the multiregional theory of human development. Popularized by Wolpoff and his colleague John Hawks, this theory fits with the same archaeological evidence that supports the African replacement theory-it's just a very different interpretation.
Wolpoff's idea hinges on the notion that the ancestors of Neanderthals and H. sapiens didn't leave Africa as distinct groups, never to see each other again until the fateful meeting that Klein described with such horror. Instead, Wolpoff suggests, humans leaving Africa 1.8 million years ago forged a pathway that many other archaic humans walked-in both directions. Instead of embarking on several distinct migrations off the continent, humans expanded their territories little by little, essentially moving next door to their old communities rather than trekking thousands of kilometers to new homes. Indeed, the very notion of an "out of Africa" migration is based on an artificial political boundary between Africa and Asia, which would have been meaningless to our ancestors. They expanded to fill the tropical forests they loved, which happened to stretch across Africa and Asia during many periods in human evolution. Early humans would have been drifting back and forth between Africa, Asia, and Europe for hundreds of thousands of years. It was all just forest to Neanderthals and H. sapiens.
If scientists like Wolpoff are right-and Hawks has presented compelling genetic evidence to back them up-then H. sapiens probably didn't march out of Africa all at once and crush all the other humans. Instead, they evolved all over the world through an extended kinship network that may have included Neanderthals as well as other early humans like Denisovans and H. erectus.
It's important to understand that the multiregional theory does not suggest that two or three separate human lineages evolved in parallel, leading to present-day racial groups. That's a common misinterpretation. Multiregionalism describes a human migration scenario similar to those we're familiar with among humans today, where people cross back and forth between regions all the time. For multiregionalists, there were never two distinct waves of immigration, with one leading to Neanderthals, and the other packed with H. sapiens hundreds of thousands of years later. Instead, the migration (and evolution) of H. sapiens started 1.8 million years ago and never stopped.
Many anthropologists believe that the truth lies somewhere in between African replacement and multiregionalism. Perhaps there were a few distinct waves of migration, such anthropologists will concede, but H. sapiens didn't "replace" the Neanderthals. Instead, H. sapiens bands probably assimilated their unusual cousins through the early human version of intermarriage.
Perhaps, when Neanderthals stood in the smooth stone entries to their caves and watched H. sapiens first entering their wooded valleys, they saw opportunity rather than a confusing threat. In this version of events, our ancient human siblings may have had few resources and lived a hardscrabble life, but they were H. sapiens' mental equals. They exchanged ideas with the newcomers, developed ways of communicating, and raised families together. Their hybrid children deeply affected the future of our species, with a few of the most successful Neanderthal genes drifting outward into some of the H. sapiens population. Neanderthals went extinct, but their hybrid children survived by joining us.
Whether you believe that humans exterminated or assimilated Neanderthals depends a lot on what you believe about your own species. Klein doesn't think Neanderthals were inferior humans doomed to die-he simply believes that early H. sapiens would have been more likely to kill and rape their way across Europe in a Neanderthal holocaust, rather than making alliances with the locals. As his comment about the sexual predilections of modern men makes clear, Klein is basing his theory on what he's observed of H. sapiens in the contemporary world. Tattersall amplified Klein's comments by saying that he thinks humans 40,000 years ago probably treated Neanderthals the way we treat each other today. "Today, Homo sapiens is the biggest threat to its own survival. And [the Neanderthal extinction] fits that picture," he said. Ultimately, Tattersall believes that we wiped out the Neanderthals just the way we're wiping ourselves out today.
Hawks, on the other hand, described a more complicated relationship between H. sapiens and Neanderthals. He believes that Neanderthals had the capacity to develop culture, but simply didn't have the resources.
Modern humans carry Neanderthal genes in our DNA."They made it in a world where very few of us would make it," he said, referring to the incredible cold and food scarcity in the regions Neanderthals called home. Anthropologists, according to Hawks, often ask the wrong questions of our extinct siblings: "Why didn't you invent a bow and arrow? Why didn't you build houses? Why didn't you do it like we would?" He thinks the answer isn't that the Neanderthals couldn't but that they didn't have the same ability to share ideas between groups the way H. sapiens did. Their bands were so spread out and remote that they didn't have a chance to share information and adapt their tools to life in new environments. "They were different, but that doesn't mean there was a gulf between us," Hawks concluded. "They did things working with constraints that people today have trouble understanding." Put another way, Neanderthals spent all day in often fatal battles to get enough food for their kids to eat. As a result, they didn't have the energy to invent bows and arrows in the evening. Despite these limitations, they formed their small communities, hunted collectively, cared for each other, and honored their dead.
When H. sapiens arrived, Neanderthals finally had access to the kind of symbolic communication and technological adaptations they'd never been able to develop before. Ample archaeological evidence shows that they quickly learned the skills H. sapiens had brought with them, and started using them to adapt to a world they shared with many other groups who exchanged ideas on a regular basis. Instead of being driven into extinction, they enjoyed the wealth of H. sapiens' culture and underwent a cultural explosion of their own. To put it another way, H. sapiens assimilated the Neanderthals. This process was no doubt partly coercive, the way assimilation so often is today.
More evidence for Hawks's claims comes from Neanderthal DNA. Samples of their genetic material can reveal just what happened after all that Pleistocene hanky-panky. A group of geneticists at the Max Planck Institute, led by Svante Pääbo, sequenced the genomes of a few Neanderthals who had died less than 38,000 years ago. After isolating a few genetic sequences that appear unique to Neanderthals, they found evidence that a subset of these sequences entered the H. sapiens genome after the first contact between the two peoples. Though this evidence does not prove definitively that genes flowed from Neanderthals into modern humans, it's a strong argument for an assimilationist scenario rather than extermination.
Our lineage is a patchwork quilt of many peoples and cultures who intermingled as they spread across the globe.A big question for anthropologists has been whether H. sapiens comes from a "pure" lineage that springs from a single line of hominins like Mitochondrial Eve. The more the genetic evidence piles up, however, the more likely it seems that our lineage is a patchwork quilt of many peoples and cultures who intermingled as they spread across the globe. Present-day humans are the offspring of people who survived grueling immigrations, harsh climates, and Earth-shattering disasters.
Most anthropologists are comfortable admitting that we just don't know what happened when early humans left Africa, and are used to revising their theories when new evidence presents itself. Klein's influential textbook The Human Career is full of caveats about how many of these theories are under constant debate and revision. In 2011, for example, the anthropologist Simon Armitage published a paper suggesting that H. sapiens emerged from Africa as early as 200,000 years ago, settling in the Middle East. This flies in the face of previous theories, which hold that H. sapiens didn't leave Africa until about 70,000 years ago. The story of how our ancestors emerged from their birthplaces in Africa turns out to be as complicated as a soap opera-and it likely includes just as much sex and death, too.
Who Survived to Tell the Tale?
Whether humans destroyed Neanderthals or merged with them, we're left with a basic fact of anthropological history, which is that modern humans survived and Neanderthals did not. It's possible that members of H. sapiens were better survivors than their hominin siblings because Neanderthals didn't exchange symbolic information; they were too sparse, spread out, and impoverished to achieve a cultural critical mass the way their African counterparts did. But it seems that Neanderthals were still swept up into H. sapiens' way of life in the end. Our Neanderthal siblings survive in modern human DNA because they formed intimate bonds with their new human neighbors.
Svante Pääbo, who led the Neanderthal DNA sequencing project, recently announced a new discovery that also sheds light on why H. sapiens might have been a better survivor than H. neanderthalensis. After analyzing a newly sequenced genome from a Denisovan, a hominin more closely related to Neanderthals than H. sapiens are, Pääbo's team concluded that there were a few distinct regions of DNA that H. sapiens did not share with either Neanderthals or Denisovans. Several of those regions contain genes connected to the neurological connections that humans can form in their brains. In other words, it's possible that H. sapiens' greater capacity for symbolic thought is connected to unique strands of DNA that the Neanderthals didn't have. "It makes a lot of sense to speculate that what had happened is about connectivity in the brain, because... Neanderthals had just as large brains as modern humans had," Pääbo said at a press conference in 2012 after announcing his discovery. "Relative to body size, they had even a bit larger brains [than H. sapiens]. Yet there is something special that happens with modern humans. It's sort of this extremely rapid technological cultural development and large societal systems, and so on." In other words, H. sapiens' brains were wired slightly differently than their fellow hominins. And once Neanderthals merged with H. sapiens' communities, bearing children with the new arrivals, their mixed offspring may have had brains that were wired differently, too. Looked at in this light, it's as if H. sapiens assimilated Neanderthals both biologically and culturally into an idea-sharing tradition that facilitated rapid adaptation even to extremely harsh conditions.
Early humans evolved brains that helped us spread ideas to our compatriots even as we scattered to live among new families and communities. It's possible that this connectedness-both neurological and social-is what allowed groups of H. sapiens to assimilate their siblings, the Neanderthals. Still, our storytelling abilities are also what allow us to remember these distant, strange ancestors today.
Humans' greatest strength 30,000 years ago may have been an uncanny ability to assimilate other cultures. But in more recent human history, this kind of connectedness almost did us in. Once human culture scaled up to incorporate unprecedentedly enormous populations, our appetite for assimilation spread plagues throughout the modern world, almost destroying humanity many times over. And it spawned deadly famines, too. Humanity's old community-building habits can become pathological on a mass scale. Thousands of years after the merging of Neanderthals and H. sapiens, the practices that helped us survive in pre-ice age Europe became, in some contexts, liabilities. They wiped out whole civilizations and made it necessary for us to change the structures of human community forever.
Excerpted with permission fromScatter, Adapt, and Remember: How Humans Will Survive a Mass Extinctionby Annalee Newitz. Copyright © 2013 by Annalee Newitz. Published by arrangement with Doubleday, an imprint of The Knopf Doubleday Publishing Group, a division of Random House, Inc. and Penguin Group (Canada), a division of Pearson Canada, Inc.
