What makes humans unique? Scientists have long known that humans, Neanderthals and Denisovans share some DNA, but a new study published in the journal Science Advances suggests that only a small portion of a person’s genome is shared with other humans. Between 1.5 and 7% of the modern human genome is ‘exclusively human’ and is not shared with our ancient ancestors, which puts scientists in a clearer position that the three species are not so different.
Modern humans have existed for about 350,000 years
The research analyzed the DNA of 279 people around the world and fossilized extracts of two ‘high coverage’ Neanderthal genomes, as well as a ‘high coverage’ Denisovan genome dating from around 40,000 to 50,000 years ago . One of the goals of the new work was to identify genes that are unique to modern humans; a difficult statistical problem, so the researchers developed a tool that accounted for missing data in ancient genomes.
“Instead of building a tree across the genome that shows how a group of genomes are related on average across the entire genome, we wanted to know what the ancestry of individuals looks like at specific sites in the genome,” says Schaefer. “Basically, we wanted to be able to show how they are all related at each variable position in the genome,” explains Nathan Schaefer of the University of California, San Francisco, a co-author of the work.
Small differences
What parts of the genome separate modern humans from archaic hominins? Only 1.5 to 7 percent of the modern human genome is unique to us. It is possible that a small fraction of the DNA genome may have a significant impact on what differentiates modern humans … Mutations that contribute to uniquely human characteristics are contained in a small part of the genome and appear to primarily affect genes related to brain development.
In other words, at least 93% of the modern human genome is shared between our species and the other two ancient hominins.
The researchers used a genetic analysis technique called ancestral recombination graphing to make their discovery. Using publicly available data from modern human, Neanderthal, and Denisovan genomes, they then sequenced these genomes themselves and used the aforementioned ancestral recombination graph tool to sketch a genetic tree spanning all three species.
Applied to the three species, it is mapped how they are related throughout the genome, finding shared and distinct regions.
The algorithm also highlighted which genes humans inherited from an even older ancestor, one that lived around 500,000 years ago , which eventually gave rise to our species, as well as Neanderthals and other hominins.
Referencia: An ancestral recombination graph of human, Neanderthal, and Denisovan genomes Science Advances 16 Jul 2021: Vol. 7, no. 29, eabc0776 DOI: 10.1126/sciadv.abc0776
