Being Human

Scientists have argued about what drove the Neanderthals into extinction since the day of their discovery in the 1850s. The abundance of theories for their demise—climate change, disease, starvation, war with humankind—hints that nobody knows anything for sure. Recently, however, DNA testing has upended the whole argument: it turns out that Neanderthals didn’t quite go extinct after all.

The DNA sequence of Neanderthals, published in 2010, revealed that all people of European and Asian descent have from one to four percent Neanderthal DNA inside them. That’s roughly equivalent to the amount of DNA you inherited from each great-great-great-grandparent. (Go back five generations in your family tree, and you might as well have a Neanderthal there.) Geneticists don’t know everything this DNA does, but some of it probably fortified humans against new diseases as they spread across the globe.

That surprise was just the start. Also in 2010, geneticists announced the discovery of a small girl’s knucklebone inside the Denisova cave in Siberia. The bone looked Neanderthal at first, but DNA tests revealed it instead as a new species of hominid—the first extinct species ever discovered through DNA. And these new hominids, dubbed Denisovans, also interbred with certain human groups, especially Melanesians, who first settled the Pacific islands between New Guinea and Fiji.

As scientists continue to catalog human diversity, DNA memories of other assignations will no doubt surface, and we’ll have to ascribe more and more “human” DNA to other creatures. A preliminary analysis of African DNA in 2011, for instance, found a third possible interbreeding event, with a still-undiscovered race of hominids. Overall, this work seems poised to change our understanding of where our species came from and expand our sense of what human being means.

(Adapted from Kean’s new book, The Violinist’s Thumb.)

Permission required for reprinting, reproducing, or other uses.

Sam Kean is the author of six science books, including The Disappearing Spoon and The Icepick Surgeon.


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