VOA慢速英语:新的研究提供了神秘人类物种的证据

A new study suggests that a mysterious human species mated with our own species tens of thousands of years ago in Africa.

Researchers say the study provides evidence that present-day West Africans can link about 2 to 19 percent of their genetic ancestry to an extinct human species. The study describes the species as a "ghost population."

Scientists involved in the research estimated that mating between the two species happened about 43,000 years ago.

Homo sapiens – the species of human that exists today - first appeared more than 300,000 years ago in Africa. The species later spread worldwide.

Earlier genetic research has shown that our species mated with two early human species, the Neanderthals and the Denisovans. The species have been extinct for thousands of years, but modern human populations outside Africa still carry DNA from both.

Scientists have discovered many fossil records relating to the Neanderthals and a few from the Denisovans. So far, though, very little is known about the newly identified "ghost population."

Sriram Sankararaman is a human genetics and computer science professor at the University of California, Los Angeles. He led the study, which was recently published in Science Advances.

Sankararaman told the Reuters news agency that "not much" is known about this mysterious species. "We don't know where this population might have lived, whether it corresponds to known fossils, and what its ultimate fate was," he added.

Sankararaman said the extinct species likely split off about 650,000 years ago from the evolutionary line that led to Homo sapiens.

The study used genetic data from hundreds of West Africans, including the Yoruba people of Nigeria and Benin and the Mende people of Sierra Leone. The researchers compared the data with DNA information from the Neanderthals and Denisovans.

Scientists say they uncovered DNA material in the West Africans that can best be explained by ancestral interbreeding with an unknown member of the human family tree.

Sankararaman said it is no longer necessary to consider only DNA from fossils of early human species to confirm that humans intermixed with them. "We can now see that such events took place by looking at our own DNA itself."

He added that the discovery "opens a new path in understanding the complexity of human evolutionary history in Africa, where the picture hasn't been as clear."

I'm Bryan Lynn.

Reuters news agency reported on this story. Bryan Lynn adapted the report for VOA Learning English. Ashley Thompson was the editor.

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