Early humans almost went extinct around 900,000 years ago

Thanks to advancements in genetic analysis, researchers in China and Italy have shed more light on our early ancestors.

A recent study based on a new genetic analysis technique has revealed a humbling discovery: early human ancestors nearly went extinct around 900,000 years ago, leaving only 1,280 individuals to spring our species back to a thriving population of 8bn.

Published in the journal Science yesterday (31 August), the international study conducted by researchers based in China and Italy found that this drastic reduction in our population happened much before our most direct ancestors, Homo sapiens, emerged.

“About 98.7pc of human ancestors were lost,” said study co-lead Prof Haipeng Li, a population geneticist at the Chinese Academy of Sciences in Beijing, adding that the fossil record in Africa and Eurasia between 950,000 and 650,000 years ago is patchy. “The discovery of this bottleneck may explain the chronological gap.”

Nick Asthon, an archaeologist at the British Museum in London who has published a similar study, said that he is intrigued by the tiny size our population shrunk to during the bottleneck.

“This would imply that it occupied a very localised area with good social cohesion for it to survive,” Ashton noted.

“Of greater surprise is the estimated length of time that this small group survived. If this is correct, then one imagines that it would require a stable environment with sufficient resources and few stresses to the system.”

While advances in genome sequencing have improved our understanding of population sizes for the period after modern humans emerged around 200,000 years ago, there are gaps in our understanding of population sizes among earlier human ancestors.

Now, using a new method of genetic analysis that involved constructing a complex family tree of genes, the researchers were able to reconstruct ancient population dynamics based on genetic data from modern-day humans.

“[The method] put the spotlight on the period 800,000 to 1m years ago – for which there is much unknown – in a way that hasn’t been done before,” Prof Stanley Ambrose, an anthropologist at the University of Illinois at Urbana-Champaign, told Nature.

What’s more, the team found that the population of early humans didn’t expand again for another 117,000 years. But how our ancestors were able to bounce back is still a mystery.

“It represents a key period of time during the evolution of humans. So, there are many important questions to be answered,” said co-author Dr Ziqian Hao, a population geneticist at the Shandong First Medical University and Shandong Academy of Medical Sciences in Jinan.

It is important to note that not all scientists are convinced of the accuracy of these findings. As quoted in The New York Times, Dr Stephan Schiffels from the Max Planck Institute for Evolutionary Anthropology in Germany said he was sceptical of the novel statistical methods used. “It is a bit like inferring the size of a stone that falls into the middle of the large lake from only the ripples that arrive at the shore some minutes later,” he said.  Though other scientists suggest the results are plausible.

Earlier this month, a study found that early humans who once lived in Europe may have been wiped out by a catastrophic decline in average temperatures across the continent as a result of “extreme glacial cooling”.

It seems the debates about our early ancestors will continue for some time.

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