Neanderthal and Human Brain Development Created a Divergent Evolutionary Path (Weekend Feature)



Brains of newborn human babies and Neanderthals, who became extinct about 28,000 years ago, were about the same size and appear almost identical at first. But after birth and particularly during the first year of life the differences in development are stark, according to Phillipp Gunz of the Max Planck Institute for Evolutionary Anthropology in Germany.

"There was a huge difference in the way they grew their brain compared to modern humans in the first one-and-a-half and two years," Gunz said. New discoveries in 2011 shed light on how our closest extinct relatives might have thought differently than us, and reveal details about the evolution of our brain.

To compare the two brains, scientists assembled a virtual Neanderthal brain by scanning skull fragments and comparing the computer models at different stages of growth to the human baby brain. The human brain began much more activity in neural circuitry in the first year of life, which may have helped early homo sapiens survive in the process of natural selection, the study said.

The brains of adult Neanderthals were a different shape than ours — theirs were less globular and more elongated, which was the norm for more than 2 million years of human evolution, and is seen in chimpanzees as well.

"The interesting thing is within modern humans, the size of the brain correlates only very weakly with any measure of intelligence," he said. "It's more the internal structure of the brain that is important.
"And the Neanderthal, they were smart because they had a huge brain, but we think that internal structures must have been different because they grew differently, so we don't think the Neanderthal saw the world as we do.

Neanderthals are believed to be modern humans' closest ancestor, and some scientists view both as the same species. A recent landmark genome analysis determined that humans most likely interbred with Neanderthals, and that as much as 4% of the modern human genome seems to be from Neanderthals.
A team at the University of Chicago reported that at least one gene, called microcephalin, involved in regulating brain growth (although the gene's precise role is not known), may have passed from the Neanderthal to ours.

Analyzing the gene from 89 people from around the world, the scientists discovered that a particular variant of the gene, called haplogroup D, present in 70% of the world's population, appeared in modern humans around 37,000 years ago and seemed to have been favored by natural selection, quickly spreading inside the human populations. 

Haplogroup D differed in so many bases from other variants of microcephalin that the geneticists estimated through statistical tests an age of a little more than 1 million years ago, long before Homo sapiens appeared. The team guessed that, most likely, prehistoric modern humans interbred with a now extinct hominid that carried haplogroup D, most likely Neanderthals. "The haplogroup was probably beneficial enough to spread quickly in modern human populations," said Bruce Lahn, a member of the research team. 

Neanderthals must have been not as cognitively advanced as modern humans, and the researchers suppose that this gene variant might have conferred modern humans a better adaptation to the Eurasian environments that Neandertals had occupied long before the arrival of the Homo sapiens. 
This is "the most compelling case to date for a genetic contribution of Neandertals to modern humans." said ancient DNA researcher Svante Paabo of the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany.

The Daily Galaxy via Max Planck Institute and


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