A new analysis of ancient genomes suggests that different branches of the human family tree have intervened repeatedly, and that some people carry DNA from an archaic, unknown ancestor. Melissa Hubis and Amy Williams of Cornell University and Adam Siepel of the Cold Spring Harbor Lab reported the findings in a study published Aug. 6 in PLOS Genetics,,
About 50,000 years ago, a group of people migrated outside Africa and intervened with Neanderthals in Eurasia. But this is not the only time our ancient human ancestors and their relatives have changed their DNA. The sequence of the genomes of the Neanderthals and a lesser-known ancient group, the Denizons, gave many new insights into these interrelated events and the movement of ancient human populations. In the new book, researchers have developed an algorithm for analyzing genomes that can identify segments of DNA that come from other species, even if that gene flow occurred thousands of years ago and comes from an unknown source. They used the algorithm to look at the genomes of two Neanderthals, one Denized and two African humans. Researchers have found evidence that 3 percent of the Neanderthal genome is descended from ancient humans and estimates that the crossbreeding occurred 200,000 and 300,000 years ago. In addition, 1
The new findings confirm previously reported cases of gene flow between ancient people and their relatives, and also point to new cases of crossbreeding. Given the number of these events, the researchers say that genetic exchange was possible whenever two groups overlapped in time and space. Their new algorithm solves the challenging problem of identifying small remnants of gene flow that arose hundreds of thousands of years ago, when only a handful of ancient genomes were available. This algorithm can also be useful for studying gene flow in other species where there has been a crossbreeding, such as wolves and dogs.
“What I think is exciting about this work is that it demonstrates what you can learn about deep human history by jointly reconstructing the complete evolutionary history of a collection of series by both modern humans and archaic hominins,” says the author. Adam Siepel. “This new algorithm that Melissa has developed, ARGweaver-D, is able to go further in time than any other computational method I’ve seen. It seems to be particularly powerful for detecting ancient introgression.”
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