One of the joys of working at NCSE is the chance to explore and explain cool science to interested members of the public. Such a chance happened recently when I got a note asking why the Neanderthals went extinct.
I’m not an anthropologist, and haven’t spent much time following the paleoanthropological literature, but I’ve spent a bit of time lately thinking about extinction. As Elizabeth Kolbert observes in her marvelous The Sixth Extinction, the idea of extinction is tricky to wrap your head around, and it took a long time for natural philosophers and natural historians to accept its reality.
My correspondent wondered why all earlier versions of humans are completely extinct. He felt that Neanderthals in Europe 40,000 years ago could have survived in small numbers in a few refuges, just as other species survive human contact. He also wondered whether Neanderthals occurred outside of Europe, and if he was correct that today’s human population is larger than the total number of humans of any species in the past. If so, he reasoned, that low population density should have meant less pressure on Neanderthals, and room for them to persist somehow.
Let’s start with the easy part: where were the Neanderthals? Neanderthals lived in Europe, central Asia, and Siberia. They do not seem to have crossed the Himalayas or undertaken voyages across any oceans. Some other members of the genus Homo did make it out to Indonesian islands (including Homo erectus on Java, and the island endemic H. floresensis on Flores), but I don’t believe there’s any record of them reaching the Americas or Australia, or any of the more distant Pacific islands. They died out, at least in Europe, about 40,000 years ago.
Neanderthals weren’t the only hominids around. For a lengthy stretch, there were multiple species within the genus Homo all living at the same time. The Smithsonian has a nice illustration of those periods of overlap. That chart doesn’t include the Denisovans, a population known from genetic evidence in a cave where Homo sapiens, Neanderthals, and this third species seem to have all lived, perhaps even lived together.
Indeed, the fact that we are the lone representative of this branch of the family tree is quite unusual on a paleontological scale. For most of the last few million years, there have been multiple species of hominids alive together, often co-existing to some degree in the same areas. And that fact lends some force to my correspondent’s question. If various species of Homo could coexist, then how could the arrival of modern humans cause the extinction of Neanderthals? That problem was at the core of my correspondent’s question.
For context, a quick scan of the literature, and a quick check with some anthropologist colleagues, turns up no clear consensus about why Neanderthals went extinct about 40,000 years ago. Some people argue for direct conflict between Homo sapiens and Neanderthals. Others favor the idea that Neanderthals were unable to compete as successfully for food or shelter as H. sapiens spread into the Neanderthal range. Others argue that it was probably a combination of factors, including competition (with domestic dogs giving H. sapiens a notable advantage, as Pat Shipman argues in her new book The Invaders), a changing climate, disease, and incorporation through interbreeding all playing a role.
My correspondent also asked some questions more generally addressing the plausibility of extinction by the mechanisms usually cited. All these concerns are reasonable, so I think it’s worth delving into them. The forces he identified are: competition, disease, interbreeding, and hunting. His objections (edited and paraphrased for clarity):
Animals routinely compete for resources and migrate when they are overwhelmed by other species. Given the sheer amount of land and the relatively modest number of people, there would be ample room for migration.…
Even the plagues of Europe didn’t affect the known world. Within each plague, there were those who survived. It’s hard to imagine that disease made extinct ALL previous species of humans.…
At low population density, it would be hard for each member to breed with a more advanced species of human, and no reason for members of one species to seek out a different species to breed with.…
Hunting presupposes that every Neanderthal could have been found and killed. Hunting can make species extinct locally (e.g., dodos), but less so in globally dispersed species. … Even with modern technology, attempts at genocide fail to completely extinguish races of people…
It’s true that no one of these forces is probably solely responsible for killing the last Neanderthal. But if we broaden our frame of reference a bit, we can see how any (or all) might nonetheless cause such an extinction. I’ll turn to that in part 2.
