Today, there are more than 8 billion human beings on the planet. Our species dominate Earth’s landscapes, and our activities are driving large numbers of other species to extinction. Had a researcher looked at the world sometime between 800,000 and 900,000 years ago, however, the picture would have been quite different. Using a new model called fast infinitesimal time coalescent process (FitCoal), East China Normal University’s Dr. Yi-Hsuan Pan and colleagues analyzed present-day human genomic sequences of 3,154 individuals. Their results show that human ancestors went through a severe population bottleneck with about 1,280 breeding individuals between around 930,000 and 813,000 years ago; this bottleneck lasted for about 117,000 years and brought human ancestors close to extinction. The decline appears to have coincided with both major climate change and subsequent speciation events.
Hu et al. detected a reduction in the population size of our ancestors from about 100,000 to about 1,000 individuals, which persisted for about 100,000 years. Image credit: Shanghai Institute of Nutrition and Health, Chinese Academy of Sciences.
Population size history is essential for studying human evolution.
However, ancient population size history during the Pleistocene is notoriously difficult to unravel.
To circumvent this difficulty, Dr. Pan and co-authors developed the FitCoal model that looks at divergence between gene lineages and can be used to estimate past population size.
“Our 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,” Dr. Pan said.
Using the FitCoal model, the authors analyzed present-day human genomic sequences of 3,154 individuals from 10 African and 40 non-African populations.
They detected a reduction in the population size of our ancestors from about 100,000 to about 1,280 individuals, which persisted for about 117,000 years.
“The gap in the African and Eurasian fossil records can be explained by this bottleneck in the Early Stone Age as chronologically,” said Dr. Giorgio Manzi, an anthropologist at Sapienza University of Rome.
“It coincides with this proposed time period of significant loss of fossil evidence.”
“The fact that FitCoal can detect the ancient severe bottleneck with even a few sequences represents a breakthrough,” said Dr. Yun-Xin Fu, a theoretical population geneticist at University of Texas Health Science Center at Houston.
An estimated 65.85% of current genetic diversity may have been lost due to the ancient bottleneck, and the prolonged period of minimal numbers of breeding individuals threatened humanity as we know it today.
This bottleneck appears to have coincided with glaciation events that led to changes in temperatures, severe droughts, and extinctions of other species, potentially used as food by ancient humans.
“These findings are just the start,” said Shanghai Institute of Nutrition and Health’s Dr. Haipeng Li.
“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.”
The results were published in the journal Science.
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Wangjie Hu et al. Genomic inference of a severe human bottleneck during the Early to Middle Pleistocene transition. Science, published online August 31, 2023; doi: 10.1126/science.abq7487
