By: Charles Choi, LiveScience Contributor
Published: 06/04/2013 12:14 PM EDT on LiveScience
No clear evidence suggests modern humans ate Neanderthals, much less that they did so enough to drive Neanderthals to extinction, despite recent claims from scientists in Spain.
Neanderthals were once the closest living relatives of modern humans, ranging across a vast area from Europe to western Asia and the Middle East. Their lineage went extinct about the same time modern humans expanded across the world, leading to speculation that modern humans wiped them out.
Scientists Bienvenido Martínez-Navarro and Policarp Hortolà at the Catalan Institute of Human Paleoecology and Social Evolution in Tarragona, Spain, noted the migration of modern humans across the globe may have played a role in the extinction of more than 178 of the world's largest mammal species or megafauna, such as woolly mammoths. Homo sapiens can essentially be considered "a worldwide pest species," they write in the May 8 issue of the journal Quaternary International. "No other species has ever developed such a killing potential." [6 Extinct Animals That Could Be Brought Back to Life]
Humans today also hunt and eat chimpanzees, gorillas and orangutans, humans' closest remaining living relatives, the researchers noted. As such, they suggest ancient modern humans may have killed and even devoured Neanderthals to extinction to get rid of competition. There is also fossil evidence that Neanderthals at times cannibalized other Neanderthals and ancient modern humans sometimes ate other ancient modern humans, they added.
However, there is no clear evidence that ancient modern humans ever ate Neanderthals, they noted. For instance, scientists have not discovered Neanderthal bones with cut marks on them from ancient modern human stone tools.
There is even very little evidence there was any violence between ancient modern humans and Neanderthals, "and the two or three possible examples there are are controversial and can be interpreted different ways," paleoanthropologist Chris Stringer at the Natural History Museum in London, who did not take part in this study, told LiveScience. "I would not say this has been one of the mainstream arguments for why Neanderthals died out."
For instance, in Shanidar Cave in Iraq, "there's a rib wound that's suggested to be from a spear that came from above, and spear-throwing appears to be an advance linked with modern humans," Stringer said. "The problem is, we don't know if there were any modern humans in the vicinity at the time, so that could've been produced by another Neanderthal, perhaps one standing over and thrusting downward against a victim who is on the ground."
Moreover, there is growing doubt there was ever much overlap between ancient modern humans and Neanderthals. For instance, recent findings suggest Neanderthals in Europe died out thousands of years earlier than before thought, perhaps never crossing paths with modern humans there.
"Even if Neanderthals and modern humans overlapped in terms of territory, they may not have contacted each other that much," Stringer said. "When modern humans came out of Africa, they did so in quite small groups, and they were spread out."
Recent genetic evidence suggests there was some interbreeding between ancient modern humans and Neanderthals, confirming there was at least some contact. "However, while such interactions could've been violent encounters, they could also have been peaceful as well," Stringer said. "We don't know for sure." [Fight, Fight, Fight: The History of Human Aggression]
When ancient modern humans encountered Neanderthals, "it may have been near the end of their time," Stringer said. "They were rather thin on the ground by then — the level of genetic diversity we see in Neanderthals suggests their population size from Spain to Siberia was at most 20,000 people, which by modern standards would make them an endangered species, really."
"In my view of the Neanderthal disappearance, we don't need to invoke violent causes for their demise," Stringer said. "There are already two main factors they had to contend with."
The first factor is very rapid climate change.
"Most of the north Atlantic was switching from bitterly cold to nearly as warm as the present day every few thousand years, sometimes in less than a decade, and so Neanderthals had to deal with an extremely unstable climate in western Europe before modern humans arrived there," Stringer said.
Second, Neanderthals had to compete for resources with modern humans.
"Modern humans were hunting the same animals and wanting to live in the best real estate. You don't have to kill off other species intentionally — just take over their environments, take away their food, and they die without lethal warfare."
There might have been some violent encounters between ancient modern human and Neanderthal groups, or within those groups — "that's human nature, and has happened throughout history," Stringer added. "But the evidence is pretty thin that violence was a major mechanism for their disappearance."