Who We Are and How We Got Here: Ancient DNA and the New Science of the Human Past

by David Reich

the archaic people who interbred with the ancestors of New Guineans were not close relatives of the Siberian Denisovans. When we examined the genomes of present-day New Guineans and Australians, and counted the number of DNA letter differences between them and the Siberian Denisovans to estimate when their ancestors separated from a common parent population, we discovered that everywhere in the genome, the number of differences was at least what would be expected for a population split that occurred 400,000 to 280,000 years ago.13 This meant that the ancestors of the Siberian Denisovans separated from the Denisovan lineage that contributed ancestry to New Guineans two-thirds of the way back to the separation of the ancestors of Denisovans from Neanderthals. In light of the remote relationship, the two groups probably had different adaptations, which would explain how they were able to thrive in such different climates. Given the extraordinary diversity of Denisovans—with much more time separation among their populations than exists among present-day groups—it makes sense to think of them as a broad category of humans, one branch of which became the ancestors of the archaic population that interbred with New Guineans and another that became Siberian Denisovans.