Although Neanderthals' brains were similar in size to their contemporary modern human counterparts, fresh analysis of fossil data suggests that their brain structure was rather different. Results imply that larger areas of the Neanderthal brain, compared to the modern human brain, were given over to vision and movement and this left less room for the higher level thinking required to form large social groups.
Professor Robin Dunbar and Eiluned Pearce at the University of Oxford and Professor Chris Stringer FRS at the Natural History Museum looked at data from 27,000–75,000-year-old fossils, mostly from Europe and the Near East. They compared the skulls of 32 anatomically modern humans and 13 Neanderthals to examine brain size and organisation. In a subset of these fossils, they found that Neanderthals had significantly larger eye sockets, and therefore eyes, than modern humans.
The researchers calculated the standard size of fossil brains for body mass and visual processing requirements. Once the differences in body and visual system size are taken into account, the researchers were able to compare how much of the brain was left over for other cognitive functions.
Previous research by Dunbar and Pearce shows that modern humans living at higher latitudes evolved bigger vision areas in the brain to cope with the low light levels. This latest study builds on that research, suggesting that Neanderthals probably had larger eyes than contemporary humans because they evolved in Europe, whereas contemporary 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,' explains lead author Eiluned Pearce, anthropologist at the University of Oxford.
‘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, differences in brain organisation and social cognition may go a long way towards explaining why Neanderthals went extinct whereas modern humans survived.'
'The large brains of Neanderthals have been a source of debate from the time of the first fossil discoveries of this group, but getting any real idea of the "quality" of their brains has been very problematic,' says Professor Chris Stringer FRS, Research Leader in Human Origins at the Natural History Museum and co-author on the paper. 'Hence discussion has centred on their material culture and supposed way of life as indirect signs of the level of complexity of their brains in comparison with ours.
'Our study provides a more direct approach by estimating how much of their brain was allocated to cognitive functions, including the regulation of social group size; a smaller size for the latter would have had implications for their level of social complexity and their ability to create, conserve and build on innovations.'
Professor Robin Dunbar observes: ‘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.’
The relationship between absolute brain size and higher cognitive abilities has long been controversial, and this new study could explain why despite similar brain size, Neanderthal culture appears less developed than that of early modern humans, for example in relation to symbolism, ornamentation and art.