New Inference Method Reveals Severe Bottleneck in Human Population
A new study led by researchers from China, Italy, and the United States has shed light on a severe bottleneck in the human population that almost wiped out the chance for humanity as we know it today. The research, which used a novel method called FitCoal (fast infinitesimal time coalescent process), analyzed modern-day human genomic sequences from 3,154 individuals to make demographic inferences.
The findings indicate that early human ancestors went through a prolonged, severe bottleneck in which only around 1,280 breeding individuals were able to sustain a population for about 117,000 years. This bottleneck in the early to middle Pleistocene era resulted in a significant loss of genetic diversity, with an estimated 65.85% of current genetic diversity being lost.
“The fact that FitCoal can detect the ancient severe bottleneck with even a few sequences represents a breakthrough,” says senior author Yun-Xin Fu, a theoretical population geneticist at the University of Texas Health Science Center at Houston. The research has also helped explain a gap in the African/Eurasian fossil record, which coincides with the proposed time period of significant loss of fossil evidence.
The reasons for this downturn in the human ancestral population are believed to be primarily climatic, with glaciation events, changes in temperatures, severe droughts, and loss of other species potentially used as food sources for ancestral humans.
However, this bottleneck also led to a speciation event where two ancestral chromosomes converged to form what is now known as chromosome 2 in modern humans. This discovery has potentially uncovered the last common ancestor for the Denisovans, Neanderthals, and modern humans.
“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 the human brain,” says senior author Yi-Hsuan Pan, an evolutionary and functional genomics expert at East China Normal University.
While this research has provided valuable insights into early human ancestors, there are still many questions to be answered. The researchers plan to continue their investigations to uncover more details about human evolution during this transitional period.
“These findings are just the start. 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,” says senior author LI Haipeng, a theoretical population geneticist and computational biologist at Shanghai Institute of Nutrition and Health, Chinese Academy of Sciences.
The results of this study will be published online in Science on August 31, 2023. The research was jointly led by Haipeng Li at SINH-CAS and Yi-Hsuan Pan at ECNU, with important contributions from collaborators Fabio Di Vincenzo, Giorgio Manzi, and Yun-Xin Fu.