One possible explanation for the mysterious disappearance of Neanderthals about 40,000 years ago is a difference in brain power from the early modern humans (Homo sapiens) who invaded Eurasian territory and defeated them. But new research into brain mutations reveals that Neanderthals and humans were much more similar than previously thought.
The Neanderthal skull was clearly different in shape from the skulls of early modern humans. Neanderthals had longer, lower skulls, heavier brow ridges, and larger nasal openings, whereas modern humans had more spherical skulls and smaller facial features. The inside of the skull, called the endocranium, also looks different between Neanderthals and modern humans.
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Because of anatomical differences in their skulls, many experts have assumed that Neanderthals were less able to speak than humans, had poor planning skills, and had limited short-term memory. Problematically, however, these differences “were not put into the context of collective variation in modern human brain anatomy, which is known to be substantial,” the researchers wrote.
To better understand changes in brain anatomy, the researchers compared two large MRI datasets of living people’s brains: 100 Han Chinese and 100 Americans of European ancestry. In nearly 70% of the brain regions the researchers assessed, the differences in brain volume between the Chinese brain group and the Americans were found to be greater than previously found between Neanderthals and early modern humans.
“This evidence does not support the idea that Neanderthals had significantly different brains and cognitive abilities compared to anatomically modern humans existing at the time,” Schoenemann told Live Science via email.
If experts assume that differences among modern human populations are not evolutionarily significant, the researchers write, then similar brain differences between Neanderthals and early modern humans are also not evolutionarily significant.
The researchers noted that even small differences in behavior or brain size can have significant evolutionary implications. One of the biggest brain differences between Neanderthals and Homo sapiens has been found to be correlated with attention and inhibition, suggesting that Neanderthals may have had slightly lower executive function abilities. However, Schoenemann said, “The correlation between brain anatomy and cognition is very weak, and even if the differences in brain anatomy were true, the implied cognitive differences would be very small.”
Because Neanderthals disappeared relatively soon after modern humans arrived, “it is unclear whether such small differences actually contributed meaningfully to Neanderthal replacement,” the researchers wrote. Given that human brains are more divergent among modern populations today than Neanderthals, and given that the brains of early modern humans diverged about 40,000 years ago, researchers do not believe that Neanderthals went extinct because they lacked the intelligence to adapt.
The new study “strongly points to demographic and genetic admixture, perhaps as a result of some kind of cultural difference, rather than innate differences in cognitive ability, as the most likely cause of Neanderthal replacement,” the researchers wrote. This idea that the genes of a minority species are overwhelmed by the genes of a majority species reflects recent work modeling the integration of Homo sapiens into the Neanderthal population, which may have disappeared within just 10,000 years.
The researchers concluded that because they only compared Chinese and American brains, further research along these lines may be warranted.
“It is very likely that even greater differences exist between modern humans, further calling into question the evolutionary significance of anatomical differences in the brains of anatomically modern Homo sapiens and putative Neanderthals,” the researchers wrote.
Editor’s note: This article was updated at 4:36 p.m. EDT to include a quote from the study’s lead author, Tom Schoenemann.
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