Human ancestors came through survival crisis 900,000 years ago: study
SHANGHAI -- Scientists have found that early human ancestors survived a huge crisis that drove them to the brink of extinction about 900,000 years ago. Roughly 98.7 percent of our ancestral population was lost at the beginning of the "bottleneck" incident, with only approximately 1,280 breeding individuals left to sustain a population for about 117,000 years, revealed a study published on Friday in the journal Science. A group of scientists from China, Italy and the United States developed a new genomic method called FitCoal capable of inferring past population size, and used the model to analyze genomic sequences from 3,154 people from African and non-African populations. The findings indicated that early human ancestors went through a prolonged and severe bottleneck that might have curtailed the genetic diversity of modern humans by nearly 66 percent, and this event was consistent with the fusion of two progenitor chromosomes, presently identified as chromosome 2 in extant human populations. This decline coincided with climate changes that turned glaciation into long-term events, a decrease in marine surface temperatures, and a possible long period of drought in Africa and Eurasia. It helps explain the loss of African and Eurasian fossil evidence in the Early Stone Age, according to the study. Also, the ancestral struggle between 930,000 and 813,000 years ago happened at a time when many scientists think the last common ancestor of modern Homo sapiens and their cousins Neanderthals and Denisovans lived. "The novel finding opens a new field in human evolution because it evokes many questions, such as the places where these individuals lived, how they overcame the catastrophic climate changes, and whether natural selection during the bottleneck had accelerated the evolution of the human brain," said the paper's senior author Pan Yi-Hsuan from East China Normal University. The researchers suggested that the control of fire and the climate shifting to be more hospitable for human life could have contributed to a later rapid population increase. "These findings are just the start," said the paper's senior author Li Haipeng with Shanghai Institute of Nutrition and Health under the Chinese Academy of Sciences. "We plan to paint a more complete picture of human evolution during this transition period to unravel the mystery of early human ancestry and evolution," said Li.