Only 7% of our DNA is unique in modern humans

What makes humans unique? Scientists have taken another step toward solving an eternal mystery with a new tool that may allow a more accurate comparison of the DNA of modern humans with that of our extinct ancestors.

According to a study published Friday in the journal Science Advances, only 7 percent of our genome is unique and has no common features with other humans or other early ancestors.

Nathan Schaefer, a computational biologist at UCLA and co-author of the new work, said:

“It’s a pretty small percentage. That’s why scientists dismiss the idea that we humans are so different from Neanderthals.”

The study used DNA extracted from the fossil remains of now-extinct Neanderthals and Denisovans dating back some 40,000 or 50,000 years, as well as from 279 modern humans from around the world.

Scientists already know that modern humans share DNA with Neanderthals, but that different people have different parts of the genome. One of the goals of the new study was to identify genes that are unique to modern humans.

It’s a difficult statistical task, and the researchers “have developed a valuable tool that accounts for missing data in ancient genomes,” said John Hawkes, a paleoanthropologist at the University of Wisconsin-Madison.

The researchers also found that an even smaller portion of our genome – just 1.5 percent – is both unique to our species and common to all living humans today. These areas of DNA may contain the most important clues about what really sets modern humans apart.

“We can say that these regions of the genome are highly enriched in genes related to neural development and brain function,” says co-author Richard Green, a computational biologist at the University of California, Santa Cruz.

In 2010, Green helped compile the first draft of the Neanderthal genome sequence. Four years later, geneticist Joshua Akey co-authored a paper showing that modern humans carry some remnants of Neanderthal DNA. Since then, scientists have continued to improve methods for extracting and analyzing genetic material from fossils.

“Better tools allow us to ask more and more detailed questions about human history and evolution,” said Akey, who now works at Princeton and was not involved in the new study. He praised the methodology of the new study.

The findings underscore that “we’re actually a very young species,” Akey said. “It wasn’t that long ago that we shared the planet with other human species.”

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