A new study based on genomic data from 3,154 modern humans suggests that nearly a million years ago, humanity’s ancestors experienced a severe population bottleneck that reduced their numbers from approximately 100,000 to just 1,280 breeding individuals.
Lasting for 117,000 years, this dramatic population decline of 98.7 percent could have led to human extinction, but we’re here today, which indicates that our ancestors survived this crisis. Geneticists Haipeng Li of the Chinese Academy of Sciences and Yi-Hsuan Pan of East China Normal University led the study.
The ancient bottleneck appears to explain a gap in the human fossil record in the Pleistocene, where there is limited evidence of human populations during this period. Anthropologist Giorgio Manzi of Sapienza University of Rome notes that the bottleneck coincides with the time of the significant loss of fossil evidence in Africa and Eurasia.
WHAT LED TO THE BOTTLENECK
Population bottlenecks, characterized by a significant reduction in a population’s numbers, can result from various events such as wars, famine, or climate crises. More recent human population bottlenecks have been documented, including one in the Northern Hemisphere around 7,000 years ago.
To analyze this ancient population bottleneck, the research team developed a new method called the fast infinitesimal time coalescent process (FitCoal), which allowed them to examine the genomic data of individuals from around the world. Their findings point to a significant population bottleneck occurring around 930,000 to 813,000 years ago, resulting in a loss of up to 65.85 percent of genetic diversity.
The exact cause of this bottleneck remains uncertain, but it coincides with a period known as the Mid-Pleistocene Transition, marked by significant changes in Earth’s glaciation cycles. Climate upheavals during this time could have led to harsh conditions, such as famine and conflict that further reduced human populations.
This ancient bottleneck may also have contributed to the fusion of two chromosomes to form human chromosome 2, which sets humans apart from other hominids who have 24 chromosomes. The formation of chromosome 2 is considered a speciation event that influenced human evolution.
The study’s authors believe that these findings open new avenues for research in human evolution, prompting questions about where these ancient individuals lived, how they survived catastrophic climate changes, and whether natural selection during the bottleneck accelerated the evolution of the human brain.
Haipeng Li notes that this discovery is just the beginning, and future research aims to provide a more comprehensive understanding of human evolution during this transitional period in the Early to Middle Pleistocene, shedding light on the mysteries of early human ancestry and evolution.
