Nearly a million years ago, a cataclysmic event nearly wiped out humanity’s ancestors.
Genomic data from 3,154 modern humans suggest a population decline from about 100,000 to only 1,280 breeding individuals about 900,000 years ago. This represents a staggering 98.7% population decline, lasting 117,000 years, and could have led to the extinction of humanity.
The fact that we are here today, in such a large number, is evidence that this is not the case. But the findings, according to a team led by geneticists Haiping Li of the Chinese Academy of Sciences and Yi-Hsuan Pan of East China Normal University in China, could explain a curious gap in the Pleistocene human fossil record.
“The gap in African and Eurasian fossil records can be explained by this bottleneck in the early Stone Age in historical terms.” Says anthropologist Giorgio Manzi Sapienza University of Rome in Italy. “It coincides with this proposed time period of significant loss of fossil evidence.”
Population bottlenecksAs is known, significant reductions in group numbers are not uncommon. When a species is destroyed by an event such as war, famine or climate crisis, the resulting decline in genetic diversity can be traced through the descendants of survivors. This way we know that there was also a human population bottleneck in the Northern Hemisphere more recently, about 7,000 years ago.
However, the further back in time you want to go, the harder it becomes to get a meaningful signal.
For this latest analysis, the research team developed a new method called fast nano-time coalescence (FitCoal) to circumvent the accumulation of numerical errors typically associated with trying to unravel these past events.
They used FitCoal to analyze genomic data from 3,154 people from around the world, from 10 African and 40 non-African populations, to look at how gene lineages have varied over time. Their results showed a major population bottleneck between about 930,000 and 813,000 years ago, which saw current genetic diversity lost by up to 65.85 percent.
In terms of the causes of the bottleneck, we will never be 100% sure of the contributing factors, but there was one key event that was happening at the time that could have played a role – Mid-Pleistocene transitional periodduring which glaciation cycles on Earth changed dramatically.
Climatic disturbances may have produced conditions that were unfavorable for human groups seeking to survive at the time, leading to famine and conflict that further reduced population numbers.
“The new discovery opens a new field in human evolution because it raises many questions.” Pan says“Such as where these individuals lived, how they overcame catastrophic climate changes, and whether natural selection during a bottleneck accelerated the evolution of the human brain.”
The bottleneck appears to have contributed to another interesting feature of the human genome: the fusion of two chromosomes to form Chromosome 2.
Humans have 23 pairs of chromosomes; Everything else Humans Those alive today – which consist of great apes – have 24. The formation of chromosome 2 appears to have been a complex process. Speciation event Which encouraged humans on a different evolutionary path.
“These results are just the beginning.” He tells me. “Future goals of this knowledge are to paint a more complete picture of human evolution during this transitional period from the Early Pleistocene to the Middle Pleistocene, which in turn will continue to unravel the mystery that is the origin and evolution of early humans.”
The research was published in Sciences.