Human evolution: origin from different groups (Introduction)

by David Turell , Monday, March 24, 2025, 16:19 (9 days ago) @ David Turell

A genetic study of human origins:

https://phys.org/news/2025-03-genetic-reveals-hidden-chapter-human.html?utm_source=nwle...

"Modern humans descended from not one, but at least two ancestral populations that drifted apart and later reconnected, long before modern humans spread across the globe.

"Using advanced analysis based on full genome sequences, researchers from the University of Cambridge have found evidence that modern humans are the result of a genetic mixing event between two ancient populations that diverged around 1.5 million years ago. About 300,000 years ago, these groups came back together, with one group contributing 80% of the genetic makeup of modern humans and the other contributing 20%.

"For the last two decades, the prevailing view in human evolutionary genetics has been that Homo sapiens first appeared in Africa around 200,000 to 300,000 years ago, and descended from a single lineage. However, these latest results, reported in the journal Nature Genetics, suggest a more complex story.

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"'Our research shows clear signs that our evolutionary origins are more complex, involving different groups that developed separately for more than a million years, then came back to form the modern human species," said co-author Professor Richard Durbin, also from the Department of Genetics.

"While earlier research has already shown that Neanderthals and Denisovans—two now-extinct human relatives—interbred with Homo sapiens around 50,000 years ago, this new research suggests that long before those interactions—around 300,000 years ago—a much more substantial genetic mixing took place.

"Unlike Neanderthal DNA, which makes up roughly 2% of the genome of non-African modern humans, this ancient mixing event contributed as much as 10 times that amount and is found in all modern humans.

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"While the researchers were able to identify these two ancestral populations, they also identified some striking changes that happened after the two populations initially broke apart.

"'Immediately after the two ancestral populations split, we see a severe bottleneck in one of them—suggesting it shrank to a very small size before slowly growing over a period of one million years," said co-author Professor Aylwyn Scally, also from the Department of Genetics.

"'This population would later contribute about 80% of the genetic material of modern humans, and also seems to have been the ancestral population from which Neanderthals and Denisovans diverged."

"'However, some of the genes from the population which contributed a minority of our genetic material, particularly those related to brain function and neural processing, may have played a crucial role in human evolution," said Cousins.

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"'What's becoming clear is that the idea of species evolving in clean, distinct lineages is too simplistic," said Cousins. "Interbreeding and genetic exchange have likely played a major role in the emergence of new species repeatedly across the animal kingdom."

'So who were our mysterious human ancestors? Fossil evidence suggests that species such as Homo erectus and Homo heidelbergensis lived both in Africa and other regions during this period, making them potential candidates for these ancestral populations, although more research (and perhaps more evidence) will be needed to identify which genetic ancestors corresponded to which fossil group.'

Comment: this extensive study tells us how various hominins may have mixed to make us as the sole surviving form. It does not satisfy dhw's quest for a full theory as to the development of bipedalism.