When the first Neanderthal bones were discovered in a cave in the Neander Valley of Germany in 1859, some scientists claimed they must be the bones of a lost Cossack who had bow legs from spending too much time on horseback. But it was soon understood that these were fossils from a species that was almost—but not quite—human. It was named Homo neanderthalensis.
Similar discoveries of Neanderthal fossils were soon made in other parts of Europe. The bones were thicker and heavier than those of Homo sapiens, and the skulls had heavy brow ridges and sloping foreheads. Scientists soon painted a picture of “Neanderthal man” as a brutish, beetle-browed, knuckle-dragging primitive with a brain that could function only at a “purely vegetative or bestial” level, as one early paleoanthropologist wrote. They lived in caves, were covered with hair, and did not have language beyond grunting and bellowing. They were opportunistic scavengers rather than noble hunters.
One curious fact, however, made it difficult to completely relegate Neanderthals to the level of beasts: they appeared to have a larger cranial capacity than Homo sapiens—their brains were bigger than ours.
This disparaging view of Neanderthals dominated scientific and popular imagination until the 1950s, when a string of discoveries in Eurasia and new, careful examinations of Neanderthal bones and artifacts led to the emergence of a more complex view of the species. The knuckle-dragging idea, for example, was shown to have come from a Neanderthal who was stooped because he suffered from crippling arthritis; Neanderthals actually walked as fully upright as we do. They were probably not covered with hair, as evidence emerged that they scraped hides and made leather pliant by chewing on skins, which meant they wore clothing—a necessity in the bitterly cold Europe of the distant past.
Studies of Neanderthal anatomy and genetics reveal that they had language ability. Not only did Neanderthals have the hyoid bone of the neck in the right position for speech, but they also carried the FOXP2 gene, which in humans is linked to speech. What’s more, they possessed an expanded Broca’s area in the brain, the region governing complex speech, the formulation of sentences, and the vocal and breath control necessary to speak words.
And their brains were indeed bigger. One of the largest hominid crania ever measured, in fact, belonged not to a modern human but to a Neanderthal who lived 55,000 years ago in what is today Israel. Neanderthal brains, however, had a smaller cerebellum and parietal lobes, which suggests that they were less capable than we are in terms of tool use, creativity, higher-order conceptualization, and social abilities. Their occipital and temporal lobes and olfactory bulbs, however, were bigger, implying they were superior to humans in smell, eyesight, and hearing. They were especially adapted to seeing in low light, and they may have been more crepuscular than diurnal—in other words, they were most active at dawn and dusk.
Far from being scavengers, Neanderthals were apex predators. They lived mostly on meat, and they hunted the most dangerous game on the planet, including mammoths, woolly rhinoceroses, aurochs, and boars, as well as wolves, cave lions, and cave bears. They had fire, with which they roasted, boiled, and smoked their food. They made houses out of mammoth bones. They flaked stone tools, although over the course of 150,000 years, their tools stayed the same, showing almost no innovation or evolution. They buried their dead. They took care of the crippled and infirm. They probably had religious beliefs and some concept of an afterlife, because they placed offerings in graves—especially those of children—and in one case, they appear to have scattered medicinal plants and flowers in an adult’s grave, which some think might mean the individual was a healer or shaman. They probably adorned themselves with shells, claws, bones, and feathers and painted their bodies. They created abstract images on cave walls, including hand stencils, dots, and lines. They collected fossils, quartz crystals, geodes, and other pretty rocks for no apparent reason except to admire their aesthetics. They had music. Fragments of bone flutes have been found at some Neanderthal sites, and the placement of the holes indicates Neanderthals may have used a pentatonic (five-note) scale. They knew how to make boats; Neanderthal tools found on Greek islands prove that they could sail short distances—but they never made the insanely dicey over-the-horizon voyages that modern humans did, such as the aborigines who used boats to reach Australia 45,000 years ago. Neanderthals were so close to us that many paleoanthropologists today think they may not have been a separate species but a subspecies.
In Europe, living in regions with a deficit of sunlight, Neanderthals probably had lighter skin color to make sufficient vitamin D. We know that at least one Neanderthal woman had red hair, and it has been theorized that the rare red-hair gene entered the modern human population through interbreeding with red-haired Neanderthals.
The gradual evolution in our understanding of Neanderthals took a revolutionary turn when it was discovered in 2010 that most of us are part Neanderthal. In that year, Svante Pääbo, an evolutionary geneticist at the Max Planck Institute for Evolutionary Anthropology in Germany, sequenced the Neanderthal genome. He and another geneticist, David Reich at Harvard, showed that Neanderthals interbred with humans. As a result, most humans carry a small percentage of Neanderthal genes, especially people from Europe and Asia. (Pääbo won the Nobel Prize in 2022 for this work.) It appears that around twenty percent of the Neanderthal genome survives in modern humans in bits and pieces, with each non-African human carrying two to four percent of Neanderthal genes.
Neanderthals were different from modern humans in important ways. One dramatic difference was in strength: Neanderthals were immensely stronger than modern humans, with much heavier bones and bigger muscles. Elizabeth Kolbert noted in “Sleeping with the Enemy,” a remarkable essay about Neanderthals in The New Yorker, that in any sort of physical contest, Neanderthals were “probably capable of beating humans to a pulp.” They had a higher metabolism and matured more quickly than modern humans. We know from assemblages of bones found in caves and group trackways that they probably lived in smaller groups than we did in our hunter-gatherer days. In 2022, the remains of a family of Neanderthals—a father, daughter, and some cousins—were found in a cave in Siberia, where they had probably starved to death during a harsh winter.
Our social interactions are without doubt one of the most complex mental activities that modern humans engage in. Even in our days as hunter-gatherers, we lived in groups large enough to require a great deal of astuteness and intelligence in navigating social relations. This may not seem obvious at first, but when you consider how difficult it is for human beings to interact effectively, get along, be productive, resolve conflicts, maintain a good reputation among peers, engage in remunerative work, navigate marriage and child-rearing, and avoid transgressing social norms, you’ll begin to see just how mentally challenging it is to be a successful human being. We devote most of our day not to solving math equations, driving cars, or writing books but to curating our interactions with others. Much of our brainpower, scientists believe, evolved to deal effectively with social interactions, which allowed us to live successfully in ever-larger groups. Chimpanzees have enormous social problems living in even small, simple troops; they are horribly prone to violence and have poor conflict resolution skills, constantly jockeying for dominance, squabbling, and beating each other up. They cooperate only with great difficulty. There is some genetic evidence that autism may be linked to atavistic Neanderthal gene variants cropping up in modern humans. One of the symptoms of autism is having difficulties in social interactions, suggesting that Neanderthals might have been similarly disadvantaged. This is one reason, perhaps, why they lived in smaller social units than modern humans—and why they could not compete when we arrived with our bigger and more cooperative groups.
What about some of the more controversial depictions in my novel, starting with cannibalism? This is also based on fact; cannibalism among Neanderthals was widespread, judging by the sheer number of sites found across Europe and Asia of cannibalized Neanderthal remains. In the French cave of Grotte de Moula-Guercy, for example, the bones of five cannibalized Neanderthals were found, in which the arms had been chopped off and disarticulated, legs stripped of flesh, and the chest cavity scooped clean of organs. In another French cave with Neanderthal remains, some thirty-five percent of the bones showed stone tool marks that indicated they had been butchered.
The practice was not limited to Neanderthals; many sites of Homo sapiens also show clear signs of cannibalism. There was, for example, widespread cannibalism in the prehistoric American Southwest, which I wrote about in an article for The New Yorker. Much of this was not starvation cannibalism—it was cannibalism employed as a tool of terror and control, a way to frighten and cow your enemies. The discovery of a peculiar gene in the human genome hints that cannibalism might have been widespread among our ancestors. Most modern humans carry variant 129 of the PRNP gene. (This is a gene that controls the manufacture of certain proteins.) Variant 129 makes humans immune to prion diseases. Prion diseases, also known as transmissible spongiform encephalopathies, are transmitted by the cannibalistic eating of human brains. The mere existence of such a gene indicates that cannibalism among our forebears might have been widespread enough to trigger pandemics of prion disease, which would cause the spread through the human population of the protective variant 129. A British investigator, Simon Underwood, noted that Neanderthals lacked variant 129. He concluded that Neanderthals, in killing and eating modern humans, might have contributed to their own extinction by being infected with human prion diseases to which they had no natural defense.
Did we drive Neanderthals to extinction? While there is no proof, the answer is almost certainly yes. When modern humans arrived in Europe is debatable, but the earliest modern human bones—found in Bulgaria, Italy, and Britain—date to around 45,000 years ago.1 Following that time, modern humans began pouring into Europe and reproducing at an ever-increasing rate. Neanderthals, who had successfully lived in Europe for over 300,000 years, went extinct 39,000 years ago—that is, around six thousand years later. The timing of our arrival and their extinction is just too close to be coincidence. How would Neanderthals have reacted to this new, ugly, and physically weaker species arriving in their lands, hunting their animals, living in their caves, fishing in their rivers, and collecting their edible and medicinal plants? And how would a migrating band of Sapiens have reacted to finding a rich valley filled with useful animals and plants, and a fine cave for living, which just happened to be occupied by some troublesome Neanderthals?
There would be violence.
The paleoanthropological world seems curiously reticent about stating outright that humans drove Neanderthals to extinction. Some researchers assert that the mass migration of modern humans from Africa simply interbred Neanderthals out of existence and assimilated them. Others point to rapid climate change as the cause of Neanderthal extinction, although Neanderthals had lived through ice ages and abrupt climate changes many times before. Some speculate that diseases brought by modern humans from Africa might have swept through Neanderthal populations, much the way European diseases decimated Indigenous populations in the New World. Some say that Neanderthal populations were so low that they were weakened from inbreeding. All these might have been contributing factors. In my view, absolutely everything we know of human history and behavior points to a violent struggle between Neanderthals and modern humans for land and resources. This has been the way of the genus Homo forever. The bottom line is that archeological digs across Europe show that when modern humans arrived in a particular region, Neanderthals soon disappeared.
As for interbreeding between Neanderthals and Sapiens, I doubt most of the Neanderthal DNA in our genome came from consensual liaisons between loving partners. Mass rape has been a tool of conflict throughout history. Violence between bands of humans of the same species is common; think how much more likely it would be between bands of different species. Human beings may have been weaker than Neanderthals, but they compensated with cleverness, cooperation, and advanced technology—and among their advantages might have been a greater sense of empathy, which is the ability to know what another person is thinking and feeling. Empathy also gives us insight into our own selves and inner motivations. As Sun Tzu wrote in The Art of War: “Know your enemy and know yourself; in a hundred battles, you will never be defeated.”
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The genomes of both Sapiens and Neanderthals record a severe genetic chokepoint some time prior to sixty thousand years ago. Both species were almost wiped out, but managed to squeak by with mere thousands or hundreds of individuals. The Sapiens population seems to have crashed to less than ten thousand “breeding pairs,” and one study estimated that the human species survived for several centuries with only around forty females at any given time of reproductive age. We don’t know where these modern humans eked out their precarious existence or whether it was one small band or a few scattered ones.
This near extinction of our species was likely caused by a single dramatic event: the Toba eruption. On the island of Sumatra, the Toba volcano exploded around 74,000 years ago in one of the largest eruptions known to have occurred on the planet. It blasted billions of tons of ash and soot into the atmosphere, which spread over the earth in a dark cloud that took perhaps six years to settle out. The dust triggered a brutal volcanic winter, freezing the earth for months, causing huge snowfalls where snow had never been, vastly increasing sea ice, killing almost all the tropical forests and many of the temperate ones, and chilling the earth for years afterward. The volcanic winter caused population crashes in other mammal species, including chimpanzees, and it appears to have triggered the extinction of some half dozen hominin species living on the earth at the time.
In the end, the Toba disaster was a gift to our species. The population crash of Sapiens was soon followed by rapid population growth, a flowering of technological innovation, and a flood of humans out of Africa and across Europe and Asia. The Toba eruption contributed to who we are, along the lines of the old adage that what doesn’t kill us makes us stronger. In clearing the earth of other hominin species, the Toba eruption left the world open to two hominin species alone, who would soon face off.2 It set the stage for the final conflict to come.
Why should we care about Neanderthals and their annihilation? Kolbert, in her Pulitzer Prize-winning book, The Sixth Extinction, lays out a convincing argument that our species is responsible for an ongoing destruction of animals and plants that is reaching the staggering levels of the earth’s previous Big Five mass extinctions. With our marvelously clever yet weirdly oblivious brains, we have managed to become an agent of mass extinction as powerful as the asteroid that wiped out the dinosaurs. It is both fascinating and troubling that the first major extinction we caused was that of our own cousins, the Neanderthals. It was the prototype of so many conflicts to come. We’ve seen across history that when two cultures meet, the stronger culture usually destroys the weaker. This is a fundamental characteristic of our species. So many of our contemporary conflicts, our tribal divisions, our clannishness, our willingness to dehumanize our opponents, our fear and hatred of the “other” are clearly rooted in our evolution. These qualities that so bedevil us today found an early and vivid expression in the deadly conflict between Sapiens and Neanderthals. If we want to know ourselves, our place on the planet, and how we must change if we wish to survive—we must also understand our Neanderthal cousins and the ancient conflict that led to their demise. And we must know Neanderthals because we are part Neanderthal. In this sense, Neanderthals did not go completely extinct but live on in our own bodies and minds.
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Will scientists bring Neanderthals back to life someday? Geneticists are already on the cusp of resurrecting several extinct creatures. The woolly mammoth and the thylacine, also known as the Tasmanian tiger, will be the first to be revivified, probably by a company called Colossal, founded by George Church, a brilliant geneticist at Harvard Medical School. The Colossal website declares: “Colossal, a bioscience and genetics company co-founded by world-renowned geneticist George Church, Ph.D., and technology entrepreneur Ben Lamm, is focused on rapidly advancing the field of species de-extinction. Using CRISPR and other genome editing technologies Colossal will pioneer a practical, working model of de-extinction to apply to the Woolly Mammoth and other species.”
In his book, Regenesis, George Church describes in detail how he would go about resurrecting Neanderthals, possibly using the services of “an extremely adventurous female human.” To accomplish this, he writes,
You’d start with a stem cell genome from a human adult and gradually reverse-engineer it into the Neanderthal genome or a reasonably close equivalent. These stem cells can produce tissues and organs. If society becomes comfortable with cloning and sees value in true human diversity, then the whole Neanderthal creature itself could be cloned by a surrogate mother chimp—or by an extremely adventurous female human.
Any technology that can accomplish such feats—taking us back into a primeval era when mammoths and Neanderthals roamed the earth—is one of unprecedented power. Genomic technologies will permit us to replay scenes from our evolutionary past and take evolution to places where it has never gone, and where it would probably never go if left to its own devices.
What a vision of the future of the human species, indeed. Church later gave an interview to Der Spiegel magazine, in which he elaborated on his views.
Der Spiegel: How do we have to imagine this: You raise Neanderthals in a lab, ask them to solve problems and thereby study how they think? Church: No, you would certainly have to create a cohort, so they would have some sense of identity. They could maybe even create a new neo-Neanderthal culture and become a political force.
Among the seed investors in Colossal are the Bitcoin billionaire twins Cameron and Tyler Winklevoss and other celebrities.
In 2022, Colossal offered a wider financing opportunity, which was swamped with money from eager investors, who oversubscribed to the offering by millions of dollars. Colossal’s efforts to de-extinct the woolly mammoth will almost certainly succeed, possibly in less than five years, and more resurrections will follow. I believe this will be a brilliant and wonderful achievement—but every extraordinary advance in technology offers a dark side. It is this dark side my novel explores.
As Church notes in his book, the same CRISPR technology being employed at Colossal to resurrect mammoths could be used to de-extinct Homo neanderthalensis. Elizabeth Kolbert, in her New Yorker article, wrote that it would be easy to put Neanderthal genes into a human embryo and see what happens—which is, of course, what I depict in my novel. She wrote: “From an experimental viewpoint, the best way to test whether any particular change is significant would be to produce a human with the Neanderthal version of the sequence. This would involve manipulating a human stem cell, implanting the genetically modified embryo into a surrogate mother, and then watching the resulting child grow up. For obvious reasons, such Island of Dr. Moreau -like research on humans is not permitted … But it is allowed on mice. Dozens of strains of mice have been altered to carry humanized DNA sequences, and new ones are being created all the time, more or less to order.” You heard that right: we’re putting human DNA into mice to see what happens. Might someone, somewhere be asking: Let’s put Neanderthal DNA into humans to see what happens?
As Frankie Cash says at the end of my novel, “If something can be done, it will be done—no matter how dangerous. I have no doubt that in China or Russia or even somewhere else in America, Neanderthals are being resurrected.”
While Extinction is fiction, the science in it is real. It is here, and it is now. If Neanderthals haven’t already been de-extincted somewhere on earth, they will be soon. Extinction is a way for me to say to readers: welcome to the Island of Dr. Moreau.
1 This picture is complicated by the fact that we know that Homo sapiens and Neanderthals were in contact with each other much earlier than that, since humans and Neanderthals interbred at least 100,000 years ago, according to genetic evidence. In my novel, I use the time period of Homo sapiens’s probable arrival in Europe, not in Asia or the Levant.
2 With the exception of some isolated populations of hominins on islands that would go extinct later.