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Ancient humanity was almost wiped out about 900,000 years ago when the global population dwindled to around 1,280 reproducing individuals, according to a new study. What’s more, the population of early human ancestors stayed this small for about 117,000 years.
The analysis, published August 31 in the journal Science, is based on a new computer model developed by a group of scientists based in China, Italy and the United States.
The statistical method used genetic information from 3,154 present-day human genomes.
Around 98.7% of human ancestors were lost, according to the study. The researchers argue that the population crash correlates with a gap in the fossil record, possibly leading to the emergence of a new hominin species that was a common ancestor of modern humans, or Homo sapiens, and Neanderthals.
“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 has accelerated the evolution of human brain,” said senior author Yi-Hsuan Pan, an evolutionary and functional genomicist at East China Normal University, in a statement.
The population bottleneck coincided with dramatic changes in climate during what’s known as the mid-Pleistocene transition, the research team suggested. Glacial periods became longer and more intense, leading to a drop in temperature and very dry climatic conditions.
Moreover, the scientists suggested that the control of fire, as well as the climate shifting to be more hospitable for human life, could have contributed to a later rapid population increase around 813,000 years ago.
The earliest evidence of the use of fire to cook food dates from 780,000 years ago in what is now modern-day Israel, the authors noted.
While ancient DNA has revolutionized our understanding about past populations, the oldest DNA from a human species dates to around 400,000 years ago.
The computer model uses the vast amount of information contained in modern human genomes about genetic variation over time to infer the size of populations at specific points in the past. The team used genetic sequences from 10 African and 40 non-African populations.
‘Provocative’ study
In a commentary on the analysis published in the same journal, Nick Ashton, curator of the Paleolithic collections at the British Museum, and Chris Stringer, research leader in human evolution at the Natural History Museum in London, described the study as “provocative.”
The two researchers, who were not involved in the study, said it brought “the vulnerability of early human populations into focus.”
However, Ashton and Stringer said that the fossil record, while sparse, did show that early human species lived in and outside Africa about 813,000 to 930,000 years ago — during the period of proposed population collapse, with fossils from that era found in what’s now China, Kenya, Ethiopia, Italy, Spain and the United Kingdom.
“Whatever caused the proposed bottleneck may have been limited in its effects on human populations outside the Homo sapiens lineage or its effects were short-lived,” the two researchers said in the commentary.
“The proposed bottleneck needs to be tested against human and archaeological evidence,” they added.