PARIS: Could the lives of the eight billion people currently on Earth have depended on the resilience of just 1,280 human ancestors who very nearly went extinct 900,000 years ago? That is the finding of a recent study which used genetic analysis modelling to determine that our ancestors teetered on the brink of annihilation for nearly 120,000 years.

However, scientists not involved in the research have criticised the claim, one said there was “pretty much unanimous” agreement among population geneticists that it was not convincing.

None denied that the ancestors of humans could have neared extinction at some point, in what is known as a population bottleneck.

But experts expressed doubts that the study could be so precise, given the extraordinarily complicated task of estimating population changes so long ago, and emphasised that similar methods had not spotted this massive population crash.

It is extremely difficult to extract DNA from the few fossils of human relatives dating from more than a couple of hundred thousand years ago, making it hard to know much about them.

But advances in genome sequencing mean that scientists are now able to analyse genetic mutations in modern humans, then use a computer model that works backwards in time to infer how populations changed — even in the distant past.

The study, published in the journal Science earlier this month, looked at the genomes of more than 3,150 modern-day humans.

The Chinese-led team of researchers developed a model to crunch the numbers, which found that the population of breeding human ancestors shrank to about 1,280 around 930,000 years ago.

Wiped out

“About 98.7 per cent of human ancestors were lost” at the start of the bottleneck, said co-author Haipeng Li of the Shanghai Institute of Nutrition and Health, Chinese Academy of Sciences. “Our ancestors almost went extinct and had to work together to survive,” he said.

The bottleneck, potentially caused by a period of global cooling, continued until 813,000 years ago, the study said.

Then there was a population boom, possibly sparked by a warming climate and “control of fire”, it added.

The researchers suggested that inbreeding during the bottleneck could explain why humans have a significantly lower level of genetic diversity compared to many other species.

The population squeeze could have even contributed to the separate evolution of Neanderthals, Denisovans and modern humans, all of which are thought to have potentially split from a common ancestor roughly around that time, the study suggested.

It could also explain why so few fossils of human ancestors have been found from the period.

However, archaeologists have pointed out that some fossils dating from the time have been discovered in Kenya, Ethiopia, Europe and China, which may suggest that our ancestors were more widespread than such a bottleneck would allow.

“The hypothesis of a global crash does not fit in with the archaeological and human fossil evidence,” the British Museum’s Nicholas Ashton told Science.

Published in Dawn, September 16th, 2023