About 900 thousand years ago, humans were on the verge of extinction.
According to the results of a genomics study published last year, the population of modern humanity's ancestors has declined to a breeding population of only 1,300 individuals in a devastating bottleneck that has pushed us to the brink of extinction. Now, a new study has found that a mass migration of humans out of Africa occurred at the same time.
This is a discovery that confirms the previous history of population decline, and indicates that the two are linked by a common denominator; An event known as Mid-Pleistocene transitional periodwhere the Earth's climate was subject to A period of absolute turmoil, Eliminate many species.
The movement of early humans from Africa to and across Europe and Asia is difficult to reconstruct. Our best evidence consists of a sparse record of bones and mostly stone artifacts, which can be difficult to date. However, evidence suggests that it was not a single event; Multiple waves of early humans and ancestors They packed up their lives and took long journeys to new environments.
Two recent studies have linked human migration to population bottlenecks, based on different types of analysis. A close reading of the human genome found that a population bottleneck caused a loss of genetic diversity about 900,000 years ago. A second study, published a few weeks later, examined early archaeological sites in Eurasia, dating the Paleolithic Bottleneck 1.1 million years ago.
This discrepancy makes it difficult to determine which climate event may have caused or at least contributed to the temporary decline in numbers, so geologists Giovanni Motoni of the University of Milan and Dennis Kent of Columbia University set out to try to narrow down the discrepancy. Timing bottleneck.
First, the researchers re-evaluated records of early human habitation sites across Eurasia, and found a group of sites reliably dating back to 900,000 years ago. In comparison, dating on older sites used as evidence of the demographic bottleneck was more ambiguous and So controversial.
They compared their findings to marine sediment records, which preserve evidence of changes in climate in the form of oxygen isotopes. The proportions of oxygen trapped in sedimentary layers indicate whether the climate was warmer or cooler at the time of mineral deposition.
Together, genomic data and hominin site history suggest that the bottleneck and migration were concurrent. During the mid-Pleistocene transition, Global ocean levels have declinedAfrica and Asia dried up, with large patches of drought emerging. Humans living in Africa were facing horrific conditions that deprived them of food and water. Fortunately, as sea levels fell, land routes to Eurasia became available, and ice skating was possible, according to the researchers' model.
Note carefully that this does not mean that humans have not migrated before. Indeed, population suffocation is at the beginning of the hadith Homo sapiens Its migration occurred at the same time as a result of climate disturbances that occurred about 900 thousand years ago.
“We suggest that enhanced dehydration during Marine isotope stage 22 Which caused the spread of savannas and arid areas across most parts of the African continent, was pushed early Homo Populations in Africa to adapt or migrate to avoid extinction. They write in their paper.
“Rapid migration in response to an acute climatic stimulus and associated means of escape are what could explain… migration out of Africa as early as 0.9 million years ago and contribute to recent genomic evidence in modern African populations experiencing a bottleneck.”
The results have been published in Proceedings of the National Academy of Sciences.
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