Close Call with Extinction: Human Ancestors Faced Precarious Future 900,000 Years Ago

close-call-with-extinction-human-ancestors-faced-precarious-future-900000-years-ago

Nearly one million years ago, a catastrophic incident nearly wiped out the progenitors of humanity.

Approximately 900,000 years ago, according to genomic data from 3,154 modern humans, the population decreased from approximately 100,000 to 1,280 reproducing individuals. This staggering 98.7 percent population decline endured 117,000 years and could have led to the extinction of humanity.

The fact that we are here today in such large numbers is evidence that it was not. According to a team led by geneticists Haipeng Li of the Chinese Academy of Sciences and Yi-Hsuan Pan of East China Normal University in China, the results would explain a perplexing lacuna in the Pleistocene human fossil record.

According to Italian anthropologist Giorgio Manzi of Sapienza University of Rome, this bottleneck in the Early Stone Age chronologically explains the fossil record divide between Africa and Eurasia. It coincides with this proposed time period of significant loss of fossil evidence.”

Population constraints, also known as significant population declines, are not uncommon. When a species is decimated by a catastrophe such as a conflict, famine, or climate crisis, the resultant decline in genetic diversity can be traced through the descendants of the survivors. This is how we know that there was also a population bottleneck in the Northern Hemisphere around 7,000 years ago, much more recently.

However, the further back in time you want to examine, the more difficult it becomes to extract a meaningful signal.

For this most recent analysis, the research team devised a new technique known as the fast infinitesimal time coalescent process (FitCoal) to circumvent the accumulation of numerical errors that is typically associated with attempting to piece together these past events.

Using FitCoal, they analyzed the genomic data of 3,154 individuals from 10 African and 40 non-African populations to determine how gene lineages diverged over time. A significant population bottleneck occurred between 930,000 and 813,000 years ago, resulting in a current genetic diversity loss of up to 65.85%.

Regarding the cause of the bottleneck, we will never know for certain what all the contributing factors were, but there was one significant event occurring at the time that could have played a role: the Mid-Pleistocene Transition, during which the Earth’s glaciation cycles changed dramatically.

It’s conceivable that climate instability could have caused unfavorable conditions for human populations struggling for survival at the time, resulting in famine and conflict that further reduced population numbers.

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Unraveling the Mysteries of Early Human Evolution

close-call-with-extinction-human-ancestors-faced-precarious-future-900000-years-ago
Nearly one million years ago, a catastrophic incident nearly wiped out the progenitors of humanity.

The novel finding opens a new field in human evolution because it evokes many questions,” says Pan, “such as the places where these individuals lived, how they overcame the catastrophic climate changes, and whether natural selection during the bottleneck has accelerated the evolution of the human brain.”

The bottleneck appears to have contributed to the fusion of two chromosomes to create chromosome 2.

Humans have 23 pairs of chromosomes, while all other living hominids, including the giant primates, have 24. The formation of chromosome 2 appears to have been a speciation event that diverted the evolution of humans.

“These findings are just the start,” says Li. “Future goals with this knowledge aim to paint a more complete picture of human evolution during this Early to Middle Pleistocene transition period, which will in turn continue to unravel the mystery that is early human ancestry and evolution.”

 

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Source: Science Alert

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