My, what big eyes those Neanderthals had! But those eyes may have been too big for their own good, according to a new study from British scientists.

Though Neanderthals and modern humans are closely related, Neanderthals are thought to have evolved from an ancestor that left Africa much earlier than the hominids that gave rise to Homo sapiens. Consequently, Neanderthal evolution was more heavily influenced by the colder and darker conditions in Europe than Homo sapiens, which spent more generations evolving more sophisticated brains before heading north. So the theory goes.

A new paper published on Wednesday in the Proceedings of the Royal Society B appears to lend credence to this theory, and also suggests that Neanderthals may have traded visual acuity for a slight decrease in a certain kind of brainpower – a gamble that later went bust in the harsh conditions of the Ice Age.

When Oxford University scientists compared the skulls of Neanderthals to the skulls of ancient modern humans, they found that the Neanderthals’ eye sockets were significantly larger – about 6 millimeters bigger from top to bottom than those of their Homo sapiens cousins.

While bigger eye sockets and larger eyes would have helped Neanderthals process visual information better, their brains likely wouldn’t have been able to devote as many resources to social skills, lead author Eiluned Pearce and her colleagues said.

"We infer that Neanderthals had a smaller cognitive part of the brain and this would have limited them, including their ability to form larger groups,” co-author Chris Stringer, a human origins expert at London’s Natural History Museum, told the BBC. “If you live in a larger group, you need a larger brain in order to process all those extra relationships.”

There’s some evidence that Homo sapiens had many kinds of interactions with Neanderthals while the two groups coexisted in Europe. Some Neanderthal DNA seems to survive in modern humans, though it’s unclear if this is the result of interbreeding or just relics from a common ancestor. One recent study cast doubt on this narrative by dating the Neanderthal extinction in Spain to tens of thousands of years before ancient humans got to Europe. But whether or not ancient humans mingled with Neanderthals, there’s no doubt which species weathered the cold better.

“While the physical response to high latitude conditions adopted by Neanderthals may have been very effective at first, the social response developed by [modern humans] seems to have eventually won out in the face of the climatic instability that characterized high-latitude Eurasia at this time,” the authors wrote.

SOURCE: Pearce et al. “New insights into differences in brain organization between Neanderthals and anatomically modern humans.” Proceedings of the Royal Society B published online 13 March 2013.