raiBig Eyes Using Too Much Brain Power Got Neanderthals Extinct

First Posted: Mar 13, 2013 03:12 PM EDT

Bigger eyes and a corresponding greater allocation of the brain to process visual information is the most recent theory about the reasons that led to the extinction of Neanderthals, our closest relatives, brought forward in a new study.

Neanderthals split from the primate line that gave rise to modern humans about 400,000 years ago. This group then moved to Eurasia and completely disappeared from the world about 30,000 years back. Other studies have shown that Neanderthals might have lived near the Arctic Circle around 31,000 to 34,000 years ago.

Genomic sequencing results, reported by the NIH, had shown that Neanderthal DNA is 99.7 percent identical to present-day human DNA and 98.8 percent identical to chimpanzee DNA. Recent study from University of Cambridge had suggested that humans and Neanderthals didn't actually inter-breed but had shared the same direct ancestor, which explains the similarity in their DNA.

Studies of the human brain employing state-of-the-art imaging technologies like real-time MRI yielded insights about the inner workings and especially the specialization of the various parts of our brain and the exact size of these areas, based on how they activate for different sensual inputs and thinking tasks.

This helps to understand the reasoning behind the most recent study on Neanderthals conducted by researchers from Natural History Museum and the University of Oxford that now suggests that despite similar brain size, the different organization of various tasks within the brain led to the disappearance of this primate line. Also, Neanderthalshad larger bodies and so their brains had to devote larger areas of brain in controlling movement. Thus, the Neanderthal brain had less space to devote to higher cognitive functioning when compared to the human brain.

For the study, researchers analyzed 64 skulls, of which 25 were Neanderthal skulls and 39 were modern human skulls. The skulls were between 27,000 and 200,000 years old.

Researchers first measured the volume inside the skull and width of eye sockets. The study team then estimated the size of the eyeball and visual cortices (brain region that controls vision). Study results showed that Neanderthals had larger eyeballs and visual cortices than humans, a trait that the researchers attribute to the habitat of the Neanderthal.

According to researchers, Neanderthals lived at high latitudes, where there is little sunshine and so the eye and the brain have to develop systems to make use of available light, which in this case are huge eyeballs and visual cortices. Even now, people living at high latitudes have larger eyeballs.

The Neanderthal brain also didn't grow over time to accommodate to changes and so had few regions devoted to cognition and understanding social structures. Researchers say that the inability to form large communities and adapt to environments, which the humans could, led to the extinction of the Neanderthals.

"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," said Prof Chris Stringer, one of the study authors from The Natural History Museum, U.K., in a news release. 

The study, New Insights into Differences in Brain Organisation between Neanderthals and Anatomically Modern Humans, is published in the Proceedings of the Royal Society B.

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