The way that the Neanderthals' brains evolved over time may have been what eventually led to their downfall, a new study suggests.
The areas of the Neanderthal brain devoted to seeing and movement were larger than those in modern humans. This may have left less space in the brain for other tasks, said a new analysis of fossils published in the journal Proceedings of the Royal Society B: Biological Sciences, on Wednesday March 13 (GMT).
How Neanderthals died out while modern humans thrived has long fired debate among anthropologists. One puzzling question is why two species with similar brain sizes evolved so differently — one dying out and the other expanding globally.
Some scientists think that violence between groups or even at the hands of modern humans could have killed off the Neanderthals, who existed up to 24,000 years ago in parts of Europe. They could have also been outcompeted by humans, who were better hunters, or wiped out by disease.
Scientists Robin Dunbar and Eiluned Pearce from the University of Oxford and Chris Stringer of the Natural History Museum in London have put forward a new theory. By comparing the skulls of several Neanderthals and modern humans, they found that though brain size was similar, the brain structures were likely very different.
The Neanderthals had much larger eye sockets, which meant they had larger eyes and would have had to devote a lot more of their brains to processing this information, a trait that's been observed in some human populations that live in lower light levels common in Northern Europe and Asia.
In the Neanderthal brain this would have cost them brain space that could have been used for planning, thinking, and social skills.
"Since Neanderthals evolved at higher latitudes and also have bigger bodies than modern humans, more of the Neanderthal brain would have been dedicated to vision and body control, leaving less brain to deal with other functions like social networking," study researcher Eiluned Pearce said in a press release from the University of Oxford.
The ability to manage large webs of complex social relationships is one of the key traits that distinguishes modern humans from the species that came before them. Everything from hunting to giving birth have been social activities for the human species.
Without the same ability, Neanderthals might have had more trouble finding support from one another in their cold, tough climate.
"Smaller social groups might have made Neanderthals less able to cope with the difficulties of their harsh Eurasian environments because they would have had fewer friends to help them out in times of need," said Pearce. "Overall, differences in brain organization and social cognition may go a long way towards explaining why Neanderthals went extinct whereas modern humans survived."