A team of scientists from the United States, Italy and China may have finally explained a major gap in the fossil record of Africa and Eurasia. This is according to a study published on August 31 in the journal Sciencethe population of human ancestors plummeted between 800,000 and 900,000 years ago.
They estimate that only 1,280 reproductively capable individuals lived during this transition between the early and middle Pleistocene. At the start of this ancestral bottleneck, which lasted about 117,000 years, about 98.7 percent of the original population was lost, according to the study.
During the late Pleistocene, modern humans spread out of Africa and other human species such as Neanderthals began to die out. The Australian continent and the Americas also saw humans for the first time, and the climate was generally cold. This period is best known for its huge ice sheets and glaciers.
An innovative method
In this study, the team used a new method called rapid infinitesimal time coalescence (FitCoal) to determine ancient demographic inferences from contemporary human genome sequences of 3,154 people.
“The fact that FitCoal can detect an ancient bottleneck even with just a few sequences is a major advance,” Yun-Xin FU, study co-author and theoretical population geneticist at the Center for Health Sciences, said in a statement. Texas at Houston.
FitCoal helped the team calculate this decline in population and genetic diversity using contemporary genome sequences from 10 African and 40 non-African populations.
“The gap in the fossil record of Africa and Eurasia can be chronologically explained by this bottleneck in the Early Stone Age,” Giorgio Manzi, an anthropologist at Sapienza University and co-author of the study, said in a statement. “It corresponds to the proposed time period of significant loss of fossil evidence.”
Loss of genetic diversity
Some of the possible reasons for this population decline are mainly related to extreme weather conditions. Temperatures changed, severe drought persisted, and food sources may have dwindled as animals such as mammoths, mastodons, and giant sloths died out. According to the study, it is estimated that 65.85% of the current genetic diversity may have been lost due to this bottleneck. The loss of genetic diversity extended the period in which the number of people who could reproduce successfully was minimal and posed a major threat to the species.
However, this bottleneck may also have contributed to speciation, which occurs when two or more species are created from a single lineage. During this speciation, the two ancestral chromosomes may have converged to form what is now chromosome 2 in modern humans. Chromosome 2 is the second largest human chromosome, comprising about 243 million base pairs of DNA. Understanding this split helped the team determine what the last common ancestor of Denisovans, Neanderthals and Homo sapiens (modern humans) might be.
“The new finding opens up a new field in human evolution because it raises many questions, such as where these individuals lived, how they overcame catastrophic climate change, and whether natural selection during the bottleneck accelerated the evolution of the human brain,” he said. in a statement by Yi-Hsuan PAN, co-author and expert in evolutionary and functional genomics at East China Normal University.
ee (popular science, scientific journal)
