A brief, highly imprecise timeline: Around 600,000 years ago, a human-like species known as the Denisovans split off from our common ancestor. Some time after that, they met and mated with members of our species, enough to impart a handful of genes that have persisted to this day. Sometime after that, they vanished, until 2008, when researchers unearthed a pinky bone belonging to one of their kind, and officially welcomed them into the human family tree.
As John Wenz noted in The Atlantic in 2014, the Denisovans—named for Denisova, the cave in Siberia’s Altay mountains where the pinky bone was found—are “the first human cousin species identified with more than fossil records.” Everything scientists know about the species comes from the DNA they left behind, in the pinky bone, previously unidentified teeth, and in modern-day Melanesians, who can trace 2 to 4 percent of their genes back to the Denisovans.
The Melanesians are the people indigenous to the cluster of Pacific islands that includes Fiji, Papua New Guinea, the Solomon Islands, and Vanuatu, among others. They are the only group of people known to have Denisovan ancestry, though by no means the only ones to carry the genes of another species. Most modern humans outside of Africa have genomes that are roughly 2 percent Neanderthal (though, in a grand tradition of Atlantic Neanderthal coverage, I think I’m obliged to note here that my colleague James Fallows is at 5 percent).