Big eyes may be beautiful, but they could be what did for the Neanderthals, say University of Oxford scientists.
Neanderthal brains were adapted to allow them to see better and maintain larger bodies - so, while they were similar in size to those of humans, their structure was rather different. Much more of the brain was given over to vision and movement, leaving less room for, well, thinking.
"Having less brain available to manage the social world has profound implications for the Neanderthals’ ability to maintain extended trading networks, and are likely also to have resulted in less well developed material culture – which, between them, may have left them more exposed than modern humans when facing the ecological challenges of the Ice Ages," says Professor Robin Dunbar.
Looking at data from 27,000–75,000-year-old fossils, mostly from Europe and the Near East, the team compared the skulls of 32 anatomically modern humans and 13 Neanderthals to examine brain size and organisation. And in some of these, they found, the Neanderthals had significantly larger eye sockets, and therefore eyes.
The researchers the worked out how much of the brain was needed for visual processing, and how much was left over for other cognitive functions.
The scientists had already established that modern humans living at higher latitudes evolved bigger vision areas in the brain, in order to cope with low light levels. They now suspect that Neanderthals probably had larger eyes than contemporary humans because they evolved in Europe, while the humans had only recently emerged from lower-latitude Africa.
"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," says Eiluned Pearce from the Institute of Cognitive and Evolutionary Anthropology.
"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."
Overall, says Pearce, these differences in brain organisation and social cognition could go a long way towards explaining why Neanderthals went extinct and humans survived.