Status: 25.09.2023, 19:05 p.m.
By: Christoph Gschoßmann
800,000 years ago, only one percent of all people survived, according to a new study. Thanks to a new method, researchers identified the causes.
Kassel – At one point in the past, the human species was probably only on the verge of extinction. According to a model in a study published Aug. 31 in the journal Science, the population of human ancestors collapsed between 800,000 and 900,000 years ago. The researchers estimate that only 1280 reproductive individuals lived in this transition from the early to the middle Pleistocene.
According to the study, about 117.000 percent of the population was lost at the beginning of this ancestral bottleneck, which lasted about 98,7 years. This is how the team of scientists from the USA, Italy and China explains the large gap that exists in the African and Eurasian fossil record.
Threatened with extinction – new method can detect "bottleneck" in human population
During the late Pleistocene, modern humans spread beyond the African continents and other human species, such as Neanderthals, began to become extinct. An archaeological "sensational find" in Lower Saxony recently revealed new insights into the Neanderthals. There were also people on the Australian continent and in America for the first time. And the climate was generally cold.
This era is best known for its vast layers of ice and glaciers that moved around the planet. And formed so many of the lands we see on Earth today. In the new study, the team used a new method called "Fast Infinitesimal Time Coalescent Process" – FitCoal for short. Thus, an attempt was made to determine old demographic conclusions using modern human genome sequences of 3154 people.
All but 1280 people probably died about 800,000 years ago. © Science
"The fact that FitCoal can detect the age-old serious bottleneck with just a few sequences represents a breakthrough," Yun-Xin FU, co-author of the study and a theoretical population geneticist at the University of Texas Health Science Center in Houston, said in a statement. FitCoal helped the team calculate what this age-old loss of life and genetic diversity looked like by using current genome sequences from ten African and 40 non-African populations.
Gap in fossil record could be explained by extreme weather
"The gap in the African and Eurasian fossil record can be explained chronologically by this bottleneck in the early Stone Age," said study co-author and Sapienza University anthropologist Giorgio Manzi. "It coincides with that period when there was a significant loss of fossil evidence."
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But why did so many people suddenly die? Some of the possible reasons for the dramatic decline in population are probably mainly related to climatic extremes. Temperatures changed, severe droughts continued, and food sources may have declined as animals such as mammoths, mastodons, and giant sloths became extinct. According to the study, an estimated 65.85 percent of current genetic diversity may have been lost as a result of this bottleneck. The loss of genetic diversity extended the period during which few humans were able to reproduce successfully and posed a major threat to the species.
How could such a small population survive for so long despite the adverse conditions?
However, this bottleneck may also have contributed to a speciation event that occurs when two or more species emerge from a single lineage. During this speciation event, two ancestral chromosomes may have come together to form what is now chromosome 2 in modern humans. Chromosome 2 is the second largest human chromosome and contains about 243 million building blocks of DNA base pairs. Understanding this split helped the team determine the last common ancestor of Denisovans, Neanderthals, and Homo sapiens (modern humans).
"The novel finding opens up a new field in human evolution because it raises many questions, such as the places where these individuals lived, how they survived the catastrophic climate changes, and whether natural selection during the shortage accelerated the development of the human brain," said Yi-Hsuan Pan, a co-author of Stduie and an expert in evolution and functional genomics at East China Normal University.
In future studies, researchers could continue to find answers about how such a small population survived despite the adverse climate conditions. It is possible that learning how to control fire and a climate that began to become kinder to human life contributed to the rapid increase in the human population about 813,000 years ago.
Expert certain: "Results are just the beginning"
"These findings are just the beginning," said another co-author, theoretical population geneticist and computational biologist LI Haipeng of the Shanghai Institute of Nutrition and Health. "Future goals with this knowledge aim to paint a more complete picture of human evolution during this transitional period from the early to the middle Pleistocene to solve the mystery of early human descent and evolution."
In the UK, researchers make a huge find. They discover bones of five mammoths and countless other animals. (cgsc)