The ancestors of modern humans were reduced to a nesting population of just 1,300 individuals in a devastating bottleneck that brought us to the brink of extinction, according to a genomics study published last year. Now a new study has shown that the mass migration of people out of Africa was happening at the same time.

This is a discovery that supports an earlier dating of population decline and suggests they share a common denominator; An event known as the mid-Pleistocene transition, in which the Earth’s climate underwent a period of complete upheaval and many species became extinct.

The movement of early humans from Africa to Europe and Asia is difficult to reconstruct. Our best evidence consists of sparse bone records and mostly stone artefacts, which can be difficult to date. But the evidence suggests that this was not a single event, but several early waves of hominid and human ancestors who made up their lives and made long journeys to new environments.

Two new studies based on different types of analysis linked human migration to population bottlenecks. Close examination of the human genome showed that a population bottleneck around 900,000 years ago led to a loss of genetic diversity. A second study, published a few weeks later, examined early archaeological sites in Eurasia and dated the bottleneck to 1.1 million years ago.

This discrepancy makes it difficult to pinpoint a climate event that could have caused or at least contributed to the temporary decline, so geologists Giovanni Muttoni of the University of Milan and Dennis Kent of Columbia University sought to narrow it down. bottleneck time.

First, the researchers reevaluated records of early hominid habitats in Eurasia and found a number of sites reliably dated to 900,000 years ago. By comparison, dating at older sites used as evidence of population bottlenecks was more uncertain and therefore controversial.

They compared their findings with records of marine sediments that preserve evidence of climate change in the form of oxygen isotopes. The proportion of oxygen trapped in sediment layers indicates whether the climate was warmer or colder when minerals were deposited.

Genomic data and hominid site dating together indicate that the bottleneck and migration occurred simultaneously. During the mid-Pleistocene transition, global ocean levels dropped and Africa and Asia dried out, leaving vast drylands. Hominids living in Africa would have faced horrific conditions that left them deprived of food and water. Fortunately, as sea levels dropped, land routes to Eurasia opened up, allowing them to travel according to the researchers’ model.

Experts point out that this does not mean that hominids did not migrate before. On the contrary, the population bottleneck of the modern ancestor homo sapiens and its migration occurred simultaneously as a result of climate changes that occurred approximately 900,000 years ago.

“We hypothesize that increased drought in Marine Isotope Stage 22, which caused the spread of savannas and arid zones across much of the African continent, challenged early populations. Homo It must adapt or migrate to avoid extinction in Africa,” they write in their paper.

“Rapid migration in response to harsh climatic factors and associated escape routes may explain migration out of Africa 0.9 million years ago and add to existing genomic evidence in modern African bottleneck populations.”