Neanderthals and modern humans living at that time had the same sized brains. But how their brains were organised may have been different. Neanderthals had larger areas dedicated to vision and control of the body, and this may have played a role in their extinction, scientists report today.
Neanderthals, who are among our closest extinct relatives, died out about 35,000 years ago. The reasons why are much debated, and this study points to clues in the brain.
Model head of a Neanderthal man
The Natural History Museum's human origins expert Prof Chris Stringer and the University of Oxford's Eiluned Pearce and Robin Dunbar compared 25 Neanderthal skulls and 39 modern human skulls, all between 27,000 and 200,000 years old.
The team analysed measurements of the inside volume of the skulls, and eye socket widths, breadths and volumes, to predict the size of the eyeballs and visual cortices (brain areas associated with vision). They found that these were larger in Neanderthals.
Neanderthals lived at high latitudes. There is less light than in the tropics, which may explain their larger visual cortices. People living at high latitudes today also have larger eyeballs and visual cortices.
Additionally, previous studies have shown that the bigger bodies of Neanderthals are associated with larger brain areas involved in body maintenance and control.
Since the Neanderthal brains didn’t grow in overall size to accommodate the larger areas dedicated to vision and control of their bodies, the team suggests the internal organisation of the brain was different.
Small group of Neanderthals - their brains may have been organised in a way that didn't allow for coordination of large social groups.
There was less brain space for areas dealing with things such as cognition, including those related to living in complex social groups.
Neanderthals may not have been able to coordinate such a large social group as modern humans. The team says this could have limited their ability to cope with environmental change and competition from early modern humans, thus playing a role in their extinction.
Stringer explains, '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. Hence discussion has centred on their material culture and reconstructed way of life as indirect signs of the level of complexity of their brains in comparison with ours.
'Recently, their possibly accelerated life history, with shorter childhoods, has been brought into the discussions, as have possible differences in brain physiology deriving from research on their DNA.
'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.'
The research paper New Insights into Differences in Brain Organisation between Neanderthals and Anatomically Modern Humans is published today in Proceedings of the Royal Society B.