Homo neanderthalensis
For ages, anthropologists have puzzled over Neanderthal and human brains, since they were the same size. If each species had comparable brainpower, why did humans dominate?

A comparison of Neanderthal and human brains has revealed it was a matter of allocation: Neanderthal brains focused more on vision and movement, leaving less room for cognition related to social networking.

According to the study, published in the journal Proceedings of the Royal Society B, bigger eyed and larger bodied Neanderthals required more brain space devoted to the visual system and basic body functions, leaving less area for what co-author Robin Dunbar called "the smart part."

He explained to Discovery News that this is "the part that is doing the creative thinking."

Dunbar, a professor of evolutionary psychology at the University of Oxford, and colleagues Eiluned Pearce and Chris Stringer compared the skulls of 32 anatomically modern humans and 13 Neanderthals. The skulls date to 27,000 to 75,000 years ago. The researchers noticed that Neanderthals had significantly larger eye sockets.

The researchers next used the known relationship between the height of the eye socket and the size of visual brain areas in living primates to estimate how much of each brain was dedicated to visual processing. Once differences in body and visual system size were taken into account, the researchers could then compare how much of the brain was left over for other types of cognition.

It's clear that environmental differences affected the evolution of each species. The common ancestor of Neanderthals and Homo sapiens was Homo heidelbergensis. It had a bulkier body, as for Neanderthals, but did not possess enlarged eyes.

"The large eyes (of Neanderthals) are purely an adaptation to low light levels, and long dark nights at higher latitudes outside the tropics," Dunbar said.

Neanderthals also tended to be shorter than humans, which again was an adaptation to colder climates since this reduces heat loss through the extremities. Modern Eskimos exhibit some of this adaptation.

Neanderthals in Europe also "developed a very confrontational and dangerous style of hunting, and were very dependent on a heavy meat diet," Dunbar shared. "Modern humans (in Africa) developed the bow and arrow, as well as spear throwers, which allowed hunting at arms' length and often focused on smaller prey."

As for what happened to the Neanderthals, some researchers believe that they were simply absorbed into the modern human population. There is evidence that, as numerous humans migrated north into Europe, they interbred with Neanderthals.

Another theory, supported by this new study, is that Neanderthals went extinct because they were less capable of forming larger social networks. Pearce theorized that "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."

She continued, "Overall, differences in brain organization and social cognition may go a long way towards explaining why Neanderthals went extinct whereas modern humans survived."

Dunbar further thinks that new diseases brought in by humans could have hurt Neanderthals. He said, "It was clear that, by the end, they were struggling to maintain a foothold in Ice Age Europe, having been squeezed down into the southern appendages of Europe (in places like Spain and Italy)."

Clive Gamble, an expert on the archaeology of human origins and a professor at Southampton University praised the new work, saying, "This paper cracks a big problem in human evolution. Neanderthals had brains as big as ours, yet did not regularly produce the sorts of cultural stuff- art, ornamentation and complicated tools -- that we take for granted...Brains got bigger, but in different ways."

"I've long argued for social differences between Neanderthals and ourselves," Gamble concluded. "It doesn't make us better than them and it doesn't confirm the age-old prejudices about stupid, brutish Neanderthals. What it does do, quite literally, is make us see them with different eyes."