All together now: did human joiners outcompete rugged Neanderthal individualists?

When dumb cooperation trumps smart self-reliance

Imagine a simulation: take two roughly equivalent bands of brainy apex primates. Endow one with hugely powerful brains and immense creativity, individuality and self-reliance. Give the other slightly smaller cranial capacity and significantly dampen its aggregate inventiveness and individuality. But then at some point in the simulation, grant this band alone an abiding compulsion to socialize and to imitate one another. Leave the two bands in a vast closed environment and come check on them again, say 500,000 years later. One will have, by any measure, thrived and been immensely fruitful. The other will have disappeared; none of its number will have been seen in the simulation for most of the last 10% of its runtime. 

This simulation could be the recent history of hominids on our planet. The also-rans we once shared it with are the Neanderthals. They had the bigger brains and their skillfully crafted artifacts show an immense creativity and individuality compared to those of our ancestors’. But we had our drives to socialize and assimilate and our compulsions to imitate and mimic, to homogenize and standardize. We became distinguished by our ever more mass societies and our hyper-efficiency where they were distinguished by their isolation and their hyper-creativity. And today, it falls to us alone to excavate our twinned storylines, one cut short tens of millennia ago, the other rolling on 8-billion strong, its innate drives to network, to copy and to join now enabled on an instantaneous, global scale.  

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40,000 years ago, our planet’s last Neanderthals disappeared. Populations in Iberia and France that had held on in the face of anatomically modern human encroachment for 10,000 years finally succumbed, vanishing from the archaeological record. This ended a half-million-year tenure of dominance across fully three-quarters of northern Eurasia; though the earliest classical Neanderthal skulls date to 250,000 years ago, the genetic evidence tells us their ancestors parted ways with ours in Africa over 500,000 years ago.

The Neanderthals’ final disappearance in northwestern Eurasia paralleled their Denisovan cousins’ demise in eastern Eurasia. Researchers have yet to positively identify Denisovan remains in East Asia's spotty and unorganized fossil record, despite recognition of their existence since 2010 when one was first sequenced from material in a Siberian cave. But odds run high that their physical remains are also already in a museum or academic cache, given that the genetics unequivocally find Denisovans to have been widespread, as attested by their having mixed with South, Southeast and East Asians in independent instances. So we know that some time before 500,000 years ago, a group of African Homo must have migrated northeast into Eurasia, and there split into two successor parties, Neanderthals who would carry on into parts north and west, and Denisovans who trekked on east, between them dominating every habitable reach of the known world outside the mother continent for hundreds of thousands of years.

But this wasn’t even all the world’s human diversity on the eve of Neanderthal extinction. On Asia’s southeast edge, paleoanthropologists find remains and tools from the diminutive Hobbits of Flores island up until some 50,000 years ago. Out on the Pacific’s western edge, in the Philippines’ northern Luzon, another small human species, Homo luzonensis, also seems to have flourished until 50,000 years ago. The discovery of these two dwarf human populations tantalizes with the growing likelihood of future discoveries still to come in the islands of Indonesia. When you add in Denisovans, this region of the world was one of the most speciose for hominins for hundreds of thousands of years (the last populations of Homo erectus in Java seem to have gone extinct only 120,000 years ago).

And then all of this changed within the space of 10,000 years, leaving our own species as what paleoanthropologist Chris Stringer calls the “lone survivors.” Our African lineage’s antecedents emerge first in the fossil record in Morocco 300,000 years ago, at the Jebel Irhoud site. But the earliest skull clearly from a modern human with no residual archaic features only appears at Ethiopia’s Omo Kibish site 233,000 years ago. Until recently, these anatomically modern humans, with gracile builds and high vaulted skulls, were thought to have only left Africa some 50,000 years ago, expanding rapidly, along the way outcompeting and extirpating all other human lineages, writing Neanderthals, Denisovans and the Hobbits out of the human story. But today we know this cannot be correct; genetic and fossil evidence for modern African-like humans in Europe and Asia appears well before the last great push outward. More than 210,000 years ago, populations with skulls more like prehistoric Africans’ than Neanderthals’ were living in and around southern Greece’s Apidima Cave. What’s more, around this time, Neanderthals also mixed with humans related to anatomically modern Africans, resulting in a telltale replacement of their original Y and mtDNA lineages.

About a generation ago, before these more nuanced realities had been fully outlined, the simplistic caricature of a single African lineage replacing all our cousins in one fell swoop 50,000 years ago had a lock on our imaginations. There were always dissenters, and many unaccounted for facts that stubbornly refused to fit the tidy account. But the narrative was strong enough to embolden Stanford paleoanthropologist Richard Klein to argue in his well-received 2002 book The Dawn of Human Culture that a macromutation 50,000 years ago first granted a single African population the ability to speak articulately, thus clearing the field of all human also-rans in just 10,000 years by dint of a newfound cultural flexibility. Over twenty years later, the combination of a richer fossil record and paleogenomics’ explosive growth has wholly undermined Klein’s posited mechanism. The expansion Klein described turns out to have been only of Eurasians and Australians; Africa itself was not initially affected. It was not even the first of the “out of Africa” expansions, in fact, it was the last of many.

But that still leaves us with the question: what happened 50,000 years ago? The Dawn of Human Culture described a real phenomenon, even if Klein’s posited biological and genetic cause doesn’t fit the facts as we know them today. In a recent interview, Harvard geneticist David Reich hazarded a hypothesis that a cultural innovation, unconditioned on any biological mutation, drove this demographic explosion. In fact, Reich’s group recently posted noteworthy results showing that natural selection in the genome seems to follow at a lag in the wake of cultural and demographic change, rather than itself being the origination point of new cultural or demographic trends; one dynamic we know well is how lactase persistence as a biological adaptation post-dates by millennia the innovation of dairy consumption. And Reich is among the most eminent geneticists working in the area of human population history, so even his speculative or first-run assessments of emerging data carry significant weight. So what is he getting at? Human history and archaeology show evidence of rapid and explosive demographic changes that seem inexplicable, but could very plausibly and persuasively have been the outcome of technological or cultural shifts consigned to confounding invisibility in the genomic record. When all the evidence comes in, we will probably see that at some earlier date, cultural happenstance drove some particular set of relevant biological adaptations here, which eventually fed into a virtuous circle, in short order leaving our ancestors the globe’s lone survivors.

The aliens like us

A major trend in paleoanthropology over the last twenty years has been the humanization of Neanderthals. That such a campaign was even called for is ironic, given that they are our own species’ nearest kin. But this cultural shift and course correction has been driven by a finding in genetics. In 2010, it became very clear that most humans had some Neanderthal ancestry, with the contribution to our DNA derived directly from this population averaging around 2%. Because of the phenomenon of negative selection against hybridization within the genome, geneticists generally assume the initial proportion of Neanderthal ancestry averaged closer to 10% (Reich recently even mooted a high estimate of 20%). Once ‌modern populations were known to have Neanderthal ancestry, it wasn’t long before Neanderthals were depicted more sympathetically, with gentle expressions, fair skin, blue eyes and red hair. Archaeologists also now believe that Neanderthals were capable of artistic production, something which the field had denied for decades. Finally, we can acknowledge that Neanderthals buried their dead, a ritual whose observance perhaps reflects an awareness of the ephemerality of life, not unlike our species’ own.

But recently, French archaeologist Ludovic Slimak, who has been working at Neanderthal sites for decades, has been making the case that we are now overcorrecting too far in this direction, blurring genuine differences between Neanderthals and anatomically modern humans, turning our cousins into pale reflections of ourselves, and thereby missing the opportunity to gain genuine insights into human minds alien in ways we can scarcely conceive of. One of Slimak’s most provocative contentions is that Neanderthal and anatomically modern human tool-making traditions were fundamentally different. Though Neanderthals made effective tools, they were never standardized, skillfully and cunningly fashioned, yes, but always seeming to reflect creative choices by their individual makers. Tools created by our anatomically modern ancestors have a monotonous but efficient uniformity that distinguishes them from Neanderthal blades. In Slimak’s reading, the indigenous Neanderthals were individualistic artisans, while the intrusive modern humans were collective creatures, prone to producing lines of standardized tools as if they were Paleolithic factory workers.

But Slimak’s work has a broader purview than just analysis of material culture; recently his team published a paper elucidating the genetic relationships of a very late Neanderthal dating to ~45,000 years ago in southern France. The source site, Grotte Mandrin, is notable because anatomically modern humans occupied it around 54,000 years ago, four millennia before the beginning of the major expansion of modern humans across Eurasia. Eventually, Neanderthals reoccupied it. Slimak evocatively named the most well-preserved individual at the site Thorin, recalling Tolkien’s character: “one of the last dwarf kings under the mountain and the last of its lineage” while “Thorin the Neanderthal is also an end of lineage. An end of a way to be human.” 

Genetics reveals the most surprising thing about Thorin: his lineage diverged from his people’s neighboring contemporary European Neanderthal populations ~105,000 years ago. For over 50,000 years, the genetic evidence shows these isolated Neanderthals did not interbreed with their nearest neighbors even a week’s walk north or east. Intriguingly, Thorin’s genome does have an affinity with some contemporaneous fellow Neanderthals from Iberia, suggesting that southwest European Neanderthals may have interacted more with each other and been a very distinct cultural and genetic group.

Previous to the discovery of the Thorin lineage, Neanderthals were generally understood to exhibit minimal population structure within any given time transect. From the Atlantic to the Siberian Altai mountains, Neanderthal remains kept telling us they had remained genetically quite homogeneous over hundreds of thousands of years. How could this have been? Long-distance gene flow that tied together disparate populations perhaps? Actually, the most persuasive answer seems to be that over the Pleistocene (2.58 million years ago to 11,700 years ago), Neanderthal populations periodically crashed, with most groups going extinct. During each subsequent population bounce-back, a lone Neanderthal population seems to have emerged as the ancestor of all subsequent ones for that cycle. For example, Neanderthals from Siberia before 100,000 years ago seem not to have been the ancestors of later populations there, which were instead genetically derived from European Neanderthals, suggesting a subsequent expansion from west to east.