Reconstruction of a specimen of Homo heidelbergensis.

Human ancestors nearly became extinct 900,000 years ago

Reconstruction of a specimen of Homo heidelbergensis.

Unknown early human species nearly died out around 900,000 years ago, according to genetic analysis. It may be both ancestors The Heidelberg Man and our ancestral species.Credit: S. Entressangle/E. Daynes/Library of Scientific Photography

Human ancestors in Africa were pushed to the brink of extinction 900,000 years ago, research shows. Work1published in Sciencesuggests a drastic reduction in the population of our ancestors before our species, Wise man, it appeared. The population was reduced to just 1,280 and did not increase again for another 117,000 years.

“About 98.7% of human ancestors were lost,” said Haipeng Li, a population geneticist at the Chinese University of Science and Technology in Beijing, who led the study. He says the fossil record in Africa and Eurasia between 950,000 and 650,000 years ago is patchy and “the discovery of this restriction could explain a chronological gap”.

Nick Ashton, an archaeologist at the British Museum in London, wrote a related opinion2, says he was impressed by the large number of people there. “This would mean that it has to take a place that lives in an environment that has good interactions in order to survive,” he said. “Even more surprising is the estimated length of time this small group survived. If this is correct, one would think it would require a stable environment with sufficient resources and less pressure on the system. “

Clues from modern DNA

To find out, researchers had to develop new tools. Advances in genome sequencing have improved scientists’ understanding of how much time has passed since modern humans evolved, but researchers are developing a method that allows them to fill in the details about early human ancestors. Serena Tucci, an anthropologist at Yale University in New Haven, Connecticut, says such work was desperately needed. “We know very little about the evolution of ancient human ancestors for a number of reasons, including methodological limitations and the difficulty of obtaining ancient DNA data. Homo examples,” he said.

The researchers’ method allowed them to reconstruct ancient human artifacts on the basis of genetic data from modern humans. By building a complex genetic family tree, the team was able to examine fine branches of the tree with precision, identifying important evolutionary events.

The technique “puts a spotlight on 800,000 to a million years ago — a lot of unknowns — in a way that’s never been done before,” said Stanley Ambrose, a paleontologist at the University of Illinois at Urbana-Champaign. .

This period was part of the Early-Middle Pleistocene transition – a period of climate change, when ice cycles became longer and more intense. In Africa, this led to long periods of drought. Li says a changing climate could have wiped out human ancestors and forced new human species to emerge. Ultimately, these may have evolved into the last ancestor of modern humans and our extinct relatives, the Denisovans and Neanderthals.

About 813,000 years ago, early humans began to swell again. How our ancestors managed to survive, and what allowed them to flourish again, is still unclear, says Ziqian Hao, a geneticist at Shandong First Medical University and Shandong Academy of Medical Sciences in Jinan, and a co-author of the paper. However, he says the bottleneck is likely to have a significant impact on human genetic diversity, driving many important features of modern humans, such as brain size. He estimates that up to two-thirds of genetic diversity was lost. “It represents a key period in human evolution. So there are a lot of important questions that need to be answered,” he said.

Ashton would like to see the researchers’ findings supported by more archaeological and fossil evidence. The authors “suggest that the bottleneck has been a global collapse of the population”, he said, “but a number of archaeological sites outside of Africa show that this is not the case. A regional barrier may be more likely.”

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