Neanderthals doomed by vision-centered brains

Neanderthals had a characteristic "bun head" shaped skull which allowed for expanded visual processing in the back of the brain. That left them less head space for the frontal lobe, which governs social cognition. (Neanderthal Museum (Mettmann, Germany))

Neanderthals' keen vision may explain why they couldn't cope with environmental change and died out, despite having the same sized brains as modern humans, new research suggests.

The findings, published Tuesday, March 12, in the journal Proceedings of the Royal Society B, suggest that Neanderthals developed massive visual regions in their brains to compensate for Europe's low light levels. That, however, reduced the brain space available for social cognition.

"We have a social brain, whereas Neanderthals appear to have a visual brain," said Clive Gamble, an archaeologist at the University of Southampton, who was not involved in the study.

As a result, the extinct hominids had smaller social and trading networks to rely on when conditions got tough. That may have caused Neanderthals to die off around 35,000 years ago.

Brain size riddle
Just how smart Neanderthals were has been a long-standing debate.

"Either they get regarded as lumbering brutes, or the other side says, 'No, they weren't that stupid. They had enormous brains, so they must have been as smart as we are,'" said study co-author Robin Dunbar, an evolutionary psychologist at the University of Oxford.

To help solve the riddle, Dunbar and his colleagues looked at 13 Neanderthal skull fossils dating from 25,000 to 75,000 years ago and compared them with 32 anatomically modern human skeletons. The researchers noticed that some of the Neanderthal fossils had much larger eye sockets, and thus eyes, than do modern humans. [10 Odd Facts About the Brain]

Low lighting
The team concluded that Neanderthals used their oversized eyes to survive in the lower-light levels in Europe, where the northern latitude means fewer of the sun's rays hit the Earth. (Modern humans also tend to have slightly bigger eyes and visual systems at higher latitudes than those living in lower latitudes, where light levels are higher.) The researchers hypothesized that Neanderthals must, therefore, also have had large brain regions devoted to visual processing.

And in fact, Neanderthal skulls suggest that the extinct hominids had elongated regions in the back of their brains, called the "Neanderthal bun," where the visual cortex lies.

"It looks like a Victorian lady's head," Dunbar told LiveScience.

Anatomically modern humans, meanwhile, evolved in Africa, where the bright light required no extra visual processing, leaving humans free to evolve larger frontal lobes.

By calculating how much brain space was needed for other tasks, the team concluded that Neanderthals had relatively less space for the frontal lobe, a brain region that controls social thinking and cultural transmission.

Isolated and dying
The findings explain why Neanderthals didn't ornament themselves or make art, Gamble told LiveScience.

These results may also help explain the Neanderthals' extinction, Dunbar said.

Smaller social brain regions meant smaller social networks. In fact, artifacts from Neanderthal sites suggest they had just a 30-mile trading radius, while human trade networks at the time could span 200 miles, Dunbar said.

With competition from humans, a bitter ice age and tiny trading networks, the Neanderthals probably couldn't access resources from better climates, which they needed in order survive, he said.

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