Severe cold temperatures may have come close to wiping out human ancestors approximately 900,000 years ago, according to a controversial DNA analysis. The study proposes that the population of these ancestors rebounded roughly 100,000 years later. This significant period of decline, occurring between around 930,000 to 813,000 years ago, coincided with extreme cold and prolonged droughts in Africa and Eurasia, as indicated by previous geological evidence.
If the findings of the new DNA-derived scenario hold true, it suggests that only a small number of survivors from the Stone Age endured to evolve into a species ancestral to Homo sapiens, Neanderthals, and Denisovans. This conclusion is proposed by population geneticist Wangjie Hu of the Icahn School of Medicine at Mount Sinai in New York City and colleagues. Their research, published in the September 1 issue of Science, indicates that before the onset of the harsh climate, the potential breeding population size ranged between 58,600 and 135,000 individuals.
Hu’s team developed a novel statistical approach to estimate the timing and sizes of ancient breeding populations using patterns of shared gene variants in modern human populations. They analyzed data from 3,154 individuals across 10 African populations and 40 non-African populations, sourced from two scientific databases of human DNA.
Their analysis concluded that a population decline among human ancestors from about 930,000 to 813,000 years ago best explained the genetic variation observed in the data. Furthermore, stronger genetic evidence of an ancient population decline was found among Africans compared to non-Africans. The researchers suggest that a diminished population of human ancestors likely existed in Africa starting around 900,000 years ago, though Eurasia cannot be ruled out as a potential region for those survivors.
As this reduced population began to recover, its members may have evolved into Homo heidelbergensis, according to Hu’s group. Some researchers view H. heidelbergensis as an ancestor of Denisovans, Neanderthals, and H. sapiens, appearing around 700,000 years ago in Africa and Eurasia.
In a comment accompanying the new study, archaeologist Nick Ashton of the British Museum in London and paleoanthropologist Chris Stringer of London’s Natural History Museum provisionally accept the new estimate of an ancient population decline among human ancestors.
However, further research is necessary to confirm these findings, particularly through genetic studies that consider ancient fluctuations in population density, geographic range, and interbreeding, according to population geneticist Aaron Ragsdale of the University of Wisconsin–Madison.
