November 22, 2011
A popular explanation for the disappearance of Neanderthals is that modern humans were superior, evolutionarily speaking. Our ancestors were smarter and more technologically advanced. When they left Africa and populated the rest of the world, the Neanderthals didn’t stand a chance.
But what if Neanderthals went extinct in part because they were too successful? New research published in the journal Human Ecology demonstrates how that’s possible. By adapting their behavior to the challenges of climate change and expanding their ranges, Neanderthals may have set up the circumstances that led to their demise.
Neanderthals emerged in Europe and West Asia by 200,000 years ago. Their close cousins, Homo sapiens, arrived in that territory sometime between 50,000 and 40,000 years ago. Within a few tens of thousands of years, Neanderthals were gone. The timing of our arrival in Eurasia and the Neanderthal extinction has led paleoanthropologists to conclude the two events are related.
Archaeologist Michael Barton of Arizona State University and his colleagues developed a new approach to studying the Neanderthal extinction, by looking at changes in land-use patterns in both Neanderthals and modern humans. They first examined 167 archaeological assemblages from across western Eurasia, from Spain to Jordan, and as far north as Romania. All of these sites date to the Late Pleistocene, 128,000 to 11,500 years ago. The team identified which species lived at which sites based on the type of artifacts; Neanderthals and humans made distinct types of stone tools.
At the beginning of the Late Pleistocene, the team discovered, both Neanderthals and modern humans tended to be nomadic, moving their camps from site to site to utilize different resources in different places. As climate became more unstable and unpredictable over time, it was harder to find resources, so both species changed their behavior: They began to travel over a larger geographic area. But instead of moving to new sites more frequently and lugging all of their stuff across greater distances, they maintained more permanent base camps and took longer, more targeted hunting and foraging trips, returning home with their bounty.
These different hunting-and-gathering strategies left their mark in the archaeological record. When Neanderthals or humans moved their camps more frequently, they tended to repair and use the same tools over and over again because it was easier to carry around fewer tools and recycle them than to bring along raw tool-making materials everywhere they went. Therefore, in archaeological sites that record nomadic behavior, archaeologists find more stone tools that have been reworked and fewer stone tools overall compared to sites that were used as more permanent base camps, where researchers find an abundance of stone tools that show little sign of being reused.
Finding that this change in behavior correlates with climate change is fascinating in its own right, but there’s another implication that relates to the question of the Neanderthal extinction. Because both humans and Neanderthals started to stray farther and farther from home to find food, they had more opportunities to come into contact with each other—more chances for mating.
In other types of animals, the researchers note, species sometimes go extinct due to breeding with closely related species, or hybridization. If one species has a larger population than the other, the less numerous species will sort of blend into the larger species. As more and more interbreeding occurs, the smaller population will eventually disappear. This may be what happened to Neanderthals, according to two population models that Barton and his colleagues developed. Under these scenarios, humans didn’t have to be better adapted to the environment (physically or culturally) than Neanderthals to win out—they just had to be more numerous. “In one sense,” the researchers write in their report, “we could say that their extinction was the result of Late Pleistocene globalization.”
Of course, it is possible that humans were more numerous and had evolutionary advantages over Neanderthals. That’s a question that requires more research and more sophisticated models. But it’s interesting to think that the Neanderthals may have sealed their fate by adapting their ranging behaviors to the changing climates of the Pleistocene. In that sense, they may have been too successful for their own good.
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