The results of my National Geographic Genographic Project are in, and they are quite interesting. It turns out that among other surprises, I am 1.7% Neanderthal and 0.4% Denisovan.
When our ancestors first migrated out of Africa around 60,000 years ago, they were not alone. At that time, at least two other species of hominid cousins walked the Eurasian landmass—Neanderthals and Denisovans. As our modern human ancestors migrated through Eurasia, they encountered the Neanderthals and interbred. Because of this, a small amount of Neanderthal DNA was introduced into the modern human gene pool.
Everyone living outside of Africa today has a small amount of Neanderthal in them, carried as a living relic of these ancient encounters. Indigenous sub-Saharan Africans have no Neanderthal DNA because their ancestors did not migrate through Eurasia.
On one level, it’s not surprising that modern humans were able to interbreed with their close cousins. According to one theory, Neanderthals, Denisovans, and modern humans are all descended from the ancient human Homo heidelbergensis. Between 300,000 to 400,000 years ago, an ancestral group of H. heidelbergensis left Africa and then split shortly after. One branch ventured northwestward into West Asia and Europe and became the Neanderthals. The other branch moved east, becoming Denisovans. By 130,000 years ago H. heidelbergensis in Africa had become Homo sapiens. Our modern human ancestors did not begin their own exodus from Africa until about 60,000 years ago, when they expanded into Eurasia and encountered their ancient cousins.
The revelation that our ancient ancestors mated with one another could help explain one of the great mysteries in anthropology: Why did the Neanderthals disappear? After first venturing out of Africa, Neanderthals thrived in Europe for several hundred thousand years. But they mysteriously died out about 30,000 years ago, roughly around the same time that modern humans arrived in Europe.
Some scientists have suggested modern humans outcompeted or outright killed the Neanderthals. But the new genetic evidence provides support for another theory: Perhaps our ancestors made love, not war, with their European cousins, and the Neanderthal lineage disappeared because it was absorbed into the much larger human population.
The Denisovans are a much more recent addition to the human family tree, and apparently to mine. In 2008, paleoanthropologists digging in a cave in southern Siberia unearthed a 40,000-year-old adult tooth and an exquisitely preserved fossilized pinkie bone that had belonged to a young girl who was between five and seven years old when she died.
Recently, scientists successfully extracted nuclear DNA from the pinkie bone and conducted comparison studies with the genomes of modern humans and Neanderthals. Studies show the girl was closely related to Neanderthals, yet distinct enough to merit classification as a new species of archaic humans, which scientists named “Denisovan” after the cave where the pinkie bone was found. The Denisovan genome also suggests the young girl had brown hair, eyes, and skin.
Surprisingly, the scientists found genetic overlap between the Denisovan genome and that of some present-day east Asians, and, in particular, a group of Pacific Islanders living in Papua New Guinea, known as the Melanesians. It appears the Denisovans contributed between 3 to 5 percent of their genetic material to the genomes of Melanesians. Scientists think that the most likely explanation is that Denisovans living in eastern Eurasia interbred with the modern human ancestors of Melanesians. When those humans crossed the ocean to reach Papua New Guinea around 45,000 years ago, they brought their Denisovan DNA over with them.
If this genetic mixing did occur, the fact that Denisovans were discovered in Siberia but contributed to the genomes of modern humans living in Southeast Asia suggests the species ranged widely across Asia, although their low genetic diversity also indicates their numbers were never very high.
My connection to ancestral cave dwellers now explains how I could survive eight years living in a 250 square foot apartment with very little to no natural light on New York’s Upper East Side.