Genomic model suggests population decline in human ancestors

AMERICAN ASSOCIATION FOR THE ADVANCEMENT OF SCIENCE (AAAS)—Between 800,000 and 900,000 years ago, the population of human ancestors crashed, according to a new genomic model* by Wangjie Hu and colleagues. They suggest that there were only about 1280 breeding individuals during this transition between the early and middle Pleistocene, and that the population bottleneck lasted for about 117,000 years. The researchers say about 98.7% of the ancestral population was lost at the beginning of the bottleneck. This decline coincided with climate changes that turned glaciations into long-term events, a decrease in marine surface temperatures, and a possible long period of drought in Africa and Eurasia. Hu et al. developed a coalescence model that looks at divergence between gene lineages and can be used to estimate past population size, using it to analyze genomic sequences from 3154 people from 10 African and 40 non-African populations. The ancient “bottleneck was directly found in all 10 African populations, but only a weak signal of the existence of such was detected in all 40 non-African populations,” Hu et al. write. The proposed bottleneck also coincided with the time that many researchers think the last common ancestor of Denisovans, Neanderthals and modern Homo sapiens lived, but the bottleneck theory needs to be tested against the archaeological and fossil human evidence, Nick Ashton and Chris Stringer write in a related Perspective. “If, as seems likely, humans were widespread inside and outside of Africa in the period between about 800-900,000 years BP … whatever caused the inferred bottleneck was limited in its effects on the wider non-sapiens lineage populations, or any effects were short-lived,” the Perspective authors add.

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