Population crash 900,000 years ago nearly killed us off

An international collaboration led by Chinese scientists has found for the first time that population collapse almost wiped out early human ancestors over 900,000 years ago, with the number of breeding individuals falling to as low as 1,280.

The sudden population decline happened during the early to middle Pleistocene era - about 930,000 years ago - probably due to changes in temperature, severe droughts and the loss of other species that were potentially used as food sources for ancestral humans, the scientists said.

The findings were the result of the scientists' use of a novel theory and calculation method called the"fast infinitesimal time coalescent process", or"FitCoal", derived from the coalescent theory. This method allowed them to determine demographic inferences by using modern-day human genomic sequences from 3,154 individuals.

A paper about their research,which may answer an unexplained gap in the African and Eurasian fossil records, was published on the website of the journal Science on Friday.

Further evidence in the research after a decade's efforts suggested that the severe population bottleneck during that era had a critical impact on human evolution, possibly determining the formation of many key phenotypes in modern humans, said Li Haipeng, a co-correspondent of the paper.

"For example, we believe that there were severe famines, and they prompted the ancestral humans to develop the capability of using and storing energy efficiently. Such capability has been imprinted into human genes for generations," said Li, who is also a theoretical population geneticist and computational biologist at the Shanghai Institute of Nutrition and Health, part of the Chinese Academy of Sciences.

"The decline in the number of ancient populations has reduced the genetic diversity of modern populations by nearly 66 percent, which has had a profound impact on human life and health," he said.

"The gap in the African and Eurasian fossil records can be explained by this bottleneck in the Early Stone Age as chronological. It coincides with this proposed time period of the significant loss of fossil evidence," said Giorgio Manzi, a senior author of the paper and an anthropologist at the Sapienza University of Rome.

Pan Yi-Hsuan, a co-correspondent of the paper and an evolutionary and functional genomics researcher at East China Normal University, said the novel finding may spur a new field in human evolution.

"It evokes many questions, such as 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,"she said.

The scientists said that these findings are just the beginning.

"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," Li said.

The research was jointly led by Li and Pan, and their collaborators from the University of Florence and the Sapienza University of Rome, both in Italy, and the University of Texas Health Science Center in the United States made important contributions.