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Were Neanderthals extinct because of the size of their brains?

Left: Skull of Homo sapiens. Right: Skull of the Neanderthal
Image: HairyMuseumMatt / Wikimedia Commons

Using computers and MRI scans, researchers have created the most detailed reconstruction of a Neanderthal brain to date, providing new insights into the social and cognitive abilities of these extinct animals. Whether these attributes are responsible for their ultimate demise, however, remains an open question.

Recent research, published today in Scientific Reports places important differences in cognitive and neuronal functions between Homo sapiens and Neanderthals led to behavioral differences that may have led to the conditions under which anatomically modern humans were successful and Neanderthals failed about 45,000 years ago. To draw this conclusion ̵

1; and in one of the first studies of its kind – scientists conducted a comparative analysis of Neanderthal and early-modern human skulls to conclude on brain function. However, with no other archaeological evidence available to support the case, and because the shape and size of brains can not be definitively linked to cognitive abilities and behaviors, the question of what caused the extinction of Neanderthals remains very unclear ,

The history of Neanderthals has puzzled archaeologists and anthropologists since the discovery of the first skeleton of its kind in 1829. Despite years of research and speculation, we are not sure what went wrong for the Neanderthals who lived in Europe, and Asia for a whopping 200,000 years, much of it during the Ice Age. At the same time, scientists are not quite sure what was right for Homo sapiens . When it comes to explaining their failure and our success, it is fair to ask: what were the differences that made the difference?

There may have been differences in the way the two species were able to adapt to rapidly changing climatic and environmental conditions. Perhaps it was also the differences in the technological, social and economic systems or in the differences in the search and hunting strategies. It is possible that Neanderthals had inferior or limited communication skills, or that Neanderthals were absorbed or wiped out by the early modern humans. These theories are all fascinating and provocative, but the last reason remains unclear.

The idea that behavioral differences might have something to do with it is not outlandish. Assuming that behavior is a function of cognitive and neurological abilities, a research team led by Naomichi Ogihara of Keio University in Japan has attempted to model the brains of Neanderthals, early anatomically modern humans, and living humans in order to derive possible functional differences between the two. Prior to this work, scientists had analyzed the differences between Neanderthals and modern human brains, but this is the first study in which brains have been reconstructed to postulate possible functional differences.

Above: Computer reconstruction of Neanderthal brains. Middle: Typical modern human brains. Bottom: Reconstructed Neanderthal brains with highlighted regions.
Photo: Takanori Kochiyama et al., 2018

In fact, although scientists have many Neanderthal skulls to work with, none of them contain actual brains that make it difficult to know how the inside of them Heads actually looked. The next best option, therefore, is to look at their fossilized skulls and try to figure out the shape, size and orientation of the Neanderthal brain.

To do this, Ogihara team created virtual three-dimensional "casts" of brains using data from the skulls of four Neanderthals and four early modern humans (the skulls used in the study were dated between 135,000 and 32,000 years ago). This allowed the researchers to reconstruct and visualize the 3D structure of the gray and white areas of the brain along with the CSF regions. Using a large set of data from the Human Connectome project, particularly MRI scans of more than 1,180 individuals, the researchers modeled the "average" human brain as the basis for the study and made a comparative analysis possible.

Using this method, the researchers uncovered "significant" differences in brain morphology. Although Neanderthals had larger skulls and thus larger overall brain volume, H. sapiens had a proportionally larger cerebellum, the part of the brain involved in higher levels of thought and action. Modern man also showed a smaller occipital region in the cerebrum, which is bound to vision. Looking at these differences, the researchers concluded such capabilities as cognitive flexibility (i.e., learning, adaptability, and unscheduled thinking), attention, speech processing, and short-term and long-term memory. Homo sapiens so the conclusion of the researchers, had better cognitive and social skills than Neanderthals and greater capacity for long-term memory and speech processing.

Comparisons of brain surface morphology in Neanderthals, formerly Homo sapiens and modern Homo sapiens.
Image: Takanori Kochiyama et al., 2018

"This team has found significant differences between Neanderthal brains and modern human brains, especially in areas of the brain that we now associate with human language skills, social collaboration, and memory capacity." said Lana Ruck, a Ph.D. student in the Cognitive Science Program of the Department of Anthropology at Indiana University, to Gizmodo. "Since these are all very adaptive behaviors that have spread in humans today compared to other species, it is interesting to see how these brain areas differed between the hominins."

Ruck, who was not involved in the new study, said this is particularly interesting in the case of Neanderthals, because the two species actually interact with each other on the landscape, and because differences in cognition are a big hypothesis for why the Neanderthals extinct, but Homo sapiens not. As the researchers concluded in the study:

The differences in cerebellar neuroanatomical organization may have led to a significant difference in the cognitive and social ability of the two species. Consequently, the ability to adapt to changing environmental conditions through innovation was limited to [Neanderthals]and this difference may have affected their chances of survival and fueled the exchange process.

Neuroscientist Kari L. Allen, Assistant Professor, Washington University School The new article is a fascinating step on the way to integrating our knowledge of modern brain functions into fossil analysis. But she said that more work is needed on the relationship between brain size, shape, and function before we can safely interpret the evolutionary impact of these differences between Neanderthals and humans.

"The authors rely on the premise that Bigger is better and that the shape of the brain surface can be used to interpret the size of brain components," said Allen Gizmodo. "One thing to keep in mind is that the overall shape of the brain is almost certainly a compromise of several factors, and some of them are likely to have little impact on perception. For example, the size and shape of the brain will increase To a certain extent limited by body size and the size and shape of the facial skull.Therefore, the connection between form and cognition is difficult to assess. "

Indeed, the notion is that we have cognitive abilities and behaviors by modeling the shape of brains in one Can extrapolate computer, at best, a poor proposal.

"That's probably the most important question, because it's a very controversial topic in the field today: what can you say about the cognitive abilities of a species if you only have their brains or skulls?" Asked jerk. "Although the authors claim that the volume of the cerebellum correlates with increased executive functions such as attention, inhibition, speech understanding and production, and working memory, this does not necessarily equate to the deficits in human subjects with smaller cerebella in their sample since the Human Connecome Data of healthy adults. "

For the same reason, Ruck said that it could play a role that smaller cerebella and reduced social and linguistic abilities in Neanderthals have a negative impact on species survival. These shortcomings aside, Ruck said the new study is one of the first attempts to predict brain surfaces and anatomy of extinct human ancestry directly from 3D computer models, "so in that sense it's important."

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As a final note, it is important to point out that brain function and intelligence are almost always a very small part of the story, and modern culture emphasizes intelligence and even makes it fetishizing Not surprisingly, some scholars attribute this to the success of early modern humans, but such an analysis tells us nothing about the culture, oral tradition, and social networks that could have helped Neanderthals cognitive "flaws" in the United States equal to H. sapiens . At the same time, this study alone can not say whether these differences have something to do with the extinction of Neanderthals. Without further information, such as archaeological or genetic evidence, the issue of the extinction of Neanderthals remains unresolved.

[Scientific Reports]

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