LUCK OF THE DRAW
HUMANS DIDN’T OUTSMART THE NEANDERTHALS. WE JUST OUTLASTED THEM
By the standards of the Paleolithic age, members of Homo neanderthalensis were the height of sophistication. These ancient hominins ranged across Europe and parts of Asia for more than 300,000 years, producing tools, jewelry and impressive cave creations.
But then Homo sapiens showed up, and the Neanderthals disappeared. So what happened?
For decades, modern human scientists assumed there must have been something wrong with the Neanderthals — or something right with us — that led to their extinction. Maybe H. neanderthalensis had bad genes that made the species more vulnerable to disease. Maybe the climate changed quickly and they couldn’t adapt. Maybe modern humans were more innovative. Acres of ancient archeological sites have been excavated and libraries of academic journals filled by scientists seeking an explanation.
“It’s like everyone is searching for ‘just so’ stories about why one species led the other to extinction,” said Oren Kolodny, an evolutionary biologist at Stanford University. But Kolodny wondered: What if there is no “just so” explanation?
In a new paper published Tuesday in the journal Nature Communications, Kolodny and his colleague Marc Feldman test a more basic hypothesis — that the extinction of the Neanderthals was simply a consequence of population dynamics and bad timing.
Neanderthals first emerged in Europe around 400,000 years ago. After evolving in Africa, anatomically modern humans arrived in Europe. There was a brief period of time, between about 51,000 and 39,000 years ago, when H. neanderthalensis and H. sapiens shared the landscape — maybe fighting, and definitely interbreeding. But at the end of that era only one species was left standing.
The speed of replacement led scientists to assume that humans had some selective advantage — a trait that made them more successful than their cousins. Initially, Kolodny was interested in calculating the size of that advantage, starting with a “null hypothesis.”
“It’s the simplest model that we can build without assuming any hard-to-prove claims, like selection or environmental change,” Kolodny explained. In other words, “What do I expect would have happened by default?”
Using what researchers already know about ancient hominin population sizes, migration patterns, and the way ecology works, Kolodny and Feldman built a simple computer model that would simulate interactions in Paleolithic Europe. At the start of the simulation, Europe is inhabited by “bands” of Neanderthals that randomly move around and die out. Every so often, a band of modern humans joins the European fray. Bands from each species have equal livelihoods of displacing the other.
Kolodny and Feldman ran their simulation hundreds of thousands of times, changing the values for a number of different variables to reflect the uncertainty that scientists have about this period of human history. But under a wide range of parameters, the simulation ended with Neanderthals dying out within 12,000 years. They just couldn’t keep up with the slow trickle of human bands that flowed continuously north from Africa.
It doesn’t necessarily prove that humans didn’t have a selective advantage, or that climate change didn’t influence their fate, Kolodny cautioned. “But even if there were no selection and no climate change, the end result would have been the same.”
EVEN IF THERE WERE NO SELECTION AND NO CLIMATE CHANGE, THE END RESULT WOULD HAVE BEEN THE SAME.