Human evolution: disappearance of Neanderthals (Introduction)

by David Turell , Monday, October 07, 2024, 14:56 (11 days ago) @ David Turell

Latest suppositions:

https://www.livescience.com/archaeology/did-we-kill-the-neanderthals-new-research-may-f...

About 37,000 years ago, Neanderthals clustered in small groups in what is now southern Spain. Their lives may have been transformed by the eruption of the Phlegraean Fields in Italy a few thousand years earlier, when the caldera's massive explosion disrupted food chains across the Mediterranean region.

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By 34,000 years ago, our closest relatives had effectively gone extinct. But because modern humans and Neanderthals overlapped in time and space for thousands of years, archaeologists have long wondered whether our species wiped out our closest relatives. This may have occurred directly, such as through violence and warfare, or indirectly, through disease or competition for resources.

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Decades of research has revealed a complex picture: A perfect storm of factors — including competition among Neanderthal groups, inbreeding and, yes, modern humans — helped erase our closest relatives from the planet.

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Now, more than 150 years of archaeological and genetic evidence makes it clear that these early human relatives were much more advanced than we originally thought. Neanderthals crafted sophisticated tools, may have made art, decorated their bodies, buried their dead, and had advanced communication abilities, albeit a more primitive kind of language than modern humans used. What's more, they survived for hundreds of thousands of years in the hostile climates of Northern Europe and Siberia.

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Based on archaeological evidence from sites from Russia to the Iberian Peninsula, Neanderthals and modern humans likely overlapped for at least 2,600 years — and perhaps as long as 7,000 years — in Europe. That overlap occurred during a bleak period in Neanderthal history that ended with their downfall — raising the question of whether modern humans were responsible for killing them off.

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The first empirical proof of that interbreeding was found in 2010, when a Neanderthal genome was sequenced. Since then, genetic analysis has shown that Neanderthals and modern humans shared much more than a geographic area — we regularly exchanged DNA back and forth, meaning there is a bit of Neanderthal in every modern human population studied to date.

When modern humans and Neanderthals met tens of thousands of years ago, the latter were probably already in trouble. Genetic studies suggest that Neanderthals had lower genetic diversity and smaller group sizes than modern humans, hinting at a potential reason for Neanderthals' demise.

"Genetically, one big clue that we get is this idea of heterozygosity," Omer Gokcumen, an evolutionary genomicist at the University at Buffalo, told Live Science...In Neanderthals' small communities, which contained fewer than 20 adults in each group, more inbreeding occurred. That meant fewer of them inherited different versions of a gene from each parent and, therefore, had low heterozygosity.

"Neanderthals may have suffered for that — what they call a mutational burden," Gokcumen said. Genetic research suggests Neanderthals had many problematic mutations that likely affected their survival. "Because of their small population size, they couldn't actually breed these bad alleles out, and their kids may actually be sickly at the end," Gokcumen said.

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while Neanderthal populations began decreasing until they became small, isolated groups without the social support necessary to care for their increasingly sickly babies, modern human groups quickly expanded through Europe.

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Nor is there genetic evidence that modern humans' diseases killed off the Neanderthals, though we do share many immune-related genes. For instance, we inherited Neanderthal genes that make us susceptible to autoimmune disorders such as lupus and Crohn's disease as well as to severe COVID-19. Future genetic analyses may reveal the potential role of disease in Neanderthals' demise, Gokcumen said.

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Neanderthal artifacts, such as pendants and etchings, show that Neanderthals were intelligent. But new research suggests there are significant differences between H. sapiens and Neanderthal brains: Modern humans have more neurons in brain regions key to higher-level thinking, and their neurons are more connected — meaning modern humans were likely more capable of thinking quickly. Combined with Neanderthals' greater difficulty in processing language, this could mean modern humans had an advantage in key tasks, Nowell said, such as hunting and foraging for food.

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"Some Neanderthal populations died out, some got massacred, some interacted and some only exchanged ideas," Sang-Hee Lee, a biological anthropologist at the University of California, Riverside, told Live Science. "The really exciting questions like 'Why did Neanderthals disappear?' 'Why did they go extinct?' no longer can have one overarching theory" she said. "Neanderthals as a whole did not have a cohesive, shared fate."

Comment: the exact story is still unknown but the above guesswork is a good summary.