Hot on the heels of the theory that Neanderthals died out because they couldn’t adapt from hunting big game to hunting rabbits comes this new theory that they died out because they developed bigger eyes than humans’ in the cold dark Northern latitudes! The theory goes like this:
Their large eyes led to too much of their brain capacity being used for processing visual information and since more of their brain capacity was also needed to handle the motion of their larger, heavier bodies, this resulted in less brain capacity being available for cognitive reasoning. They therefore had “less brain to deal with other functions like social networking” and had “fewer friends to help them out in times of need”. Obviously they then remained culturally trapped in the Stone Age and could not develop written language or Facebook or Agriculture as competing humans eventually did. Apart from a few intrepid and promiscuous Neanderthals who managed to participate in contributing their genes to the human gene pool, all the rest died out.
A novel theory but a little far-fetched!
Eiluned Pearce
This is the theory of Eiluned Pearce a DPhil student at Oxford and is published in a paper published today in the Proceedings of the Royal Society B (but where it is beyond a pay wall). A press release has been issued by the University of Oxford.
The only data are measurements of eye sockets in 13 Neanderthal skulls compared to those in 32 human skulls from the same time. All the rest is just conjecture – and then further conjecture based on the original speculation. It would seem to be a little light on data and a little heavy on conjecture. It is still an interesting conjecture nevertheless.
… Looking 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 the Oxford scientists 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 from the Institute of Cognitive and Evolutionary Anthropology 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, 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 Neanderthal culture appears less developed than that of early modern humans, for example in relation to symbolism, ornamentation and art.
The Smithsonian blog writes:
One of the easiest differences to quantify, they found, was the size of the visual cortex—the part of the brain responsible for interpreting visual information. In primates, the volume of this area is roughly proportional to the size of the animal’s eyes, so by measuring the Neanderthals’ eye sockets, they could get a decent approximation of their the visual cortex as well. The Neanderthals, it turns out, had much larger eyes than ancient humans. The researchers speculate that this could be because they evolved exclusively in Europe, which is of higher latitude (and thus has poorer light conditions) than Africa, where H. sapiens evolved.
Along with eyes, Neanderthals had significantly larger bodies than humans, with wider shoulders, thicker bones and a more robust build overall. To account for this difference, the researchers drew upon previous research into the estimated body masses of the skeletons found with these skulls and of other Neanderthals. In primates, the amount of brain capacity devoted to body control is also proportionate to body size, so the scientists were able to calculate roughly how much of the Neanderthals’ brains were assigned to this task.
After correcting for these differences, the research team found that the amount of brain volume left over for other tasks—in other words, the mental capacity not devoted to seeing the world or moving the body—was significantly smaller for Neanderthals than for ancient H. sapiens. Although the average raw brain volumes of the two groups studied were practically identical (1473.84 cubic centimeters for humans versus 1473.46 for Neanderthals), the average “corrected” Neanderthal brain volume was just 1133.98 cubic centimeters, compared to 1332.41 for the humans.
This divergence in mental capacity for higher cognition and social networking, the researcher argue, could have led to the wildly different fates of H. sapiens and Neanderthals. “Having less brain available to manage the social world has profound implications for the Neanderthals’ ability to maintain extended trading networks,” Robin Dunbar, one of the co-authors, said in a press statement. “[They] 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.”
New insights into differences in brain organization between Neanderthals and anatomically modern humans by Eiluned Pearce, Chris Stringer and R. I. M. Dunbar
Published online March 13, 2013 doi:10.1098/rspb.2013.0168 Proc. R. Soc. B 7 May 2013 vol. 280 no. 1758 20130168
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