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Study Shows Some Humans Carry Mysterious Ancestor’s DNA

Utilizing an algorithm that analyzes genomes, a group of scientists looked at the interbreeding of ancient humans with other species. They found that species belonging to different branches of our family tree interbred on many occasions. The scientists also found DNA from a mysterious ancestor, which is still present in some living people’s genomes.

ZME Science reported on the discovery, which was made by Melissa Hubisz and Amy Williams of Cornell University, and Adam Siepel of Cold Spring Harbor Laboratory. The team recently published its research in PLOS Genetics. In their paper, the scientists describe Hubisz’ “ancestral recombination graph” algorithm, dubbed ARGweaver-D. Using ARGweaver-D, Hubisz et al. were able to identify segments in Homo sapien DNA that come from other species. Even if that so-called “gene flow” took place thousands of years ago and occurred due to an unknown source.

Using ARGweaver-D, the scientists found that the Denisovans, a subspecies of archaic human—which may, in fact, be its own distinct species—have a genome that contains one percent of DNA from an unknown and more distant relative. And because the Denisovans interbred with ancestors of H. sapien, they passed on some of that mysterious relative’s genes. By the accounts of ARGweaver-D, about 15% of these “super-archaic” genetic sequences may be present in some modern humans.

“This new algorithm that Melissa has developed, ARGweaver-D, is able to reach back further in time than any other computational method I’ve seen,” Siepel told Science Daily. The computational biologist added that the algorithm is especially good at detecting ancient introgression. Introgression is the movement of genes from one species into the pool of another by way of an intermediary hybrid.

a reconstruction of a potential subspecies of H. erectus

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Although the scientists are uncertain of who the mysterious relative is, some speculate that it could be Homo erectus. H. erectus, or “upright man,” lived between approximately 1.9 million and 110,000 years ago. The picture above shows a reconstruction of a potential subspecies of H. erectus, Homo erectus georgicus.

Along with the mysterious DNA, scientists also confirmed previously reported cases of gene flow between ancient humans and their relatives. In fact, there’s apparently enough evidence at this point to think that, as Science Daily notes, “genetic exchange was likely whenever two groups overlapped in time and space.”

Gene flow map illustration

John D. Croft

In the future, researchers will use ARGweaver-D to identify more evidence of gene flow between H. sapien and other species. The algorithm will also be useful for identifying instances of interbreeding among other species, such as in wolves and dogs.

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