A new method of inferring ancient population size uncovers a potential bottleneck that may have almost eliminated the chance for continued humanity.
The researchers believe that our Pleistocene ancestors were down to just 1,280 breeding individuals.
The disputed study says that it can explain the gap in the African-Eurasian fossil record.
A group of researchers just published a paper in the journal Science claiming that there was a “severe bottleneck” in the human population chain—one so stark that human ancestors were down to about 1,280 breeding individuals 930,000 years ago, almost wiping out the human population.
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Blaming glaciation events for the plummeting of life from about 930,000 to 813,000 years ago, the international research team claims that they have created a “novel method”—the fast infinitesimal time coalescent process—to accurately determine demographic inferences.
The new research indicates a roughly 117,000-year severe population bottleneck that would have nearly eliminated Pleistocene ancestors—removing 98.7 percent of the population—before humans could really get going. That means that, according to this study, the entire current human population can be traced back to these 1,280 individuals.
“The gap in the African and Eurasian fossil records can be explained by this bottleneck in the Early Stone Age as chronologically,” Giorgio Manzi, a senior author and anthropologist at Sapienza University in Rome, said in a news release. “It coincides with this proposed time period of significant loss of fossil evidence.”
But not everyone is convinced.
“The hypothesis of a global crash does not fit in with the archaeological and human fossil evidence,” counters Nicholas Ashton, a paleolithic archaeologist at the British Museum not involved in the study, according to Science. “Questions remain as to what triggered the bottleneck, and what, after 120,000 years, led to expansion.”
The study authors believe that glaciation events changed temperatures, caused draughts, and eliminated species potentially used as food sources for the ancestral humans—all factors that would have made life difficult for those on Earth. They don’t have an explanation for the sudden boost in population that followed.
The authors claim that in the early to middle Pleistocene era—which coincides with the prolonged period of minimal breeding individuals—an estimated 65 percent of genetic diversity may have been lost.
The study also suggests that a population squeeze may have helped differentiate between Neanderthals, Denisovans, and modern humans.
“The novel finding opens a new field in human evolution because it evokes many questions, such as the places were these individuals lived, how they overcame the catastrophic climate changes, and whether natural selection during the bottleneck has accelerated the evolution of human brain,” Yi-Hsuan Pan, senior author and evolutionary and functional genomics researcher at East China Normal University, said in a news release.
The precision of the findings, though, may be a stretch, according to group leader for population genetics at Germany’s Max Planck Institute for Evolutionary Anthropology Stephan Schiffels. He told AFP that he was “extremely skeptical” that the research could pinpoint numbers so accurately, and that it will “never be possible” for such an ancient study to be certain to such an exacting figure.
The new study relies on a freshly devised computational model—looking at 3,154 modern-day human genomic sequences while extrapolating genetic mutations—to walk back in time and show that early human ancestors suffered extreme loss of life and genetic diversity.
Schiffels, according to AFP, also noted that the data used in the research isn’t new, and that no other previous models have shown a population crash.
Janet Kelso, a computational biologist at the Max Planck Institute, told Science that this bottleneck concept may not be as widespread as the authors believe, saying that the genetic signals for it are strong only in present-day African populations. This means that any potential bottleneck would have likely been limited to certain ancestral populations. The conclusions, she says, “though intriguing, should probably be taken with some caution and explored further.”
There was “a pretty much unanimous response among population geneticists, people who work in this field, that the paper was unconvincing,” Aylwyn Scalley, a Cambridge University human evolutionary genetics researcher, told AFP.
Pontus Skoglund of the Francis Crick Institute told AFP he agrees with the others questioning the research. “It is hard,” he says, “to be convinced by the conclusion.”
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