Today the entire planet is covered by people. But genetic analysis claims that our ancestors almost became extinct around 930,000 years ago. Before that, there were said to have been around 100,000 specimens; due to radical climate change, almost all of them died and only 1,280 remained of reproductive age. “Approximately 98.7 percent of human ancestors were lost at the start of the bottleneck, putting our ancestors at risk of extinction,” the scientists write in the journal Science.
The method behind the study is not new. The genetic variants in the DNA can be used to draw conclusions about ancestry and ancient populations. Thanks to advances in DNA sequencing technology, increasingly detailed insights are now possible. Each genome contains over three billion pieces of genetic information. These letters are sometimes passed down over millions of years. Neanderthal genes can still be found in people today.
Haipeng Li of the Chinese Academy of Sciences in Shanghai and his colleagues have developed their own method for reconstructing this evolution. With FitCoal (for Fast Infinitesimal Time Coalescent) they want to decipher the history of a population. They can divide millions of years of evolution into periods of months. “It’s a tool we developed to find out the history of different groups of living things, from humans to plants,” said Dr. Li. They turned to humans when there was enough data. For the study, they compared the genomes of 3,154 people from 50 populations around the world.
Their question was: How can we best explain today’s genetic diversity despite strong similarities? Their answer is a catastrophe 930,000 years ago in which almost all ancestors became extinct and only a small group survived. A kind of bottleneck in evolution in which previously great diversity is reduced only to flourish again later.
“The numbers emerging from our study correspond to those of species currently at risk of extinction,” Professor Giorgio Manzi, an anthropologist at Sapienza University in Rome and lead author of the study, told the British Guardian. “It was fortunate that we survived, but (…) we know from evolutionary biology that the emergence of a new species can certainly occur in small, isolated populations.”
The researchers believe there were around 98,000 reproductively capable individuals before the collapse. Then the population collapsed to just 1280 individuals. The group remained very small for 117,000 years, and only then did the population recover. The model would also explain why so few remains from this period have been found. There just weren’t enough people to leave many behind.
Global climate change is said to have led to the crisis. At that time the world became colder and drier, only an isolated group could survive this time. This theory is supported by the fact that the ancestors of humans separated from their relatives, the Neanderthals and Denisovans, during this period. A change in the chromosomes is also an indication. “All people with 24 pairs of chromosomes died out, while only the small isolated population with 23 pairs of chromosomes survived and was then passed down from generation to generation,” said Ziqian Hao, also an author of the study.
The findings are surprising and are rewriting human history. But the FitCoal method is still new. It remains to be seen how reliable their results will be once more DNA sequencing from humans and other species is available.
Sources: Guardian, NYT
