Chapter 18.6, Problem 1CT

The unexpected discovery that humans interbred with Neanderthals was a triumph for the experts who developed the techniques for extracting, isolating, and sequencing ancient DNA. But perhaps the most stunning revelation made possible by ancient DNA was the discovery of the Denisovans, a hominin species whose existence would still be unknown if not for analysis of its ancient DNA. The fossil fragments from which the DNA was extracted were too few, too small, and too nondescript to have even been recognized as belonging to a previously unknown species. A newfound ability to identify new extinct species on the basis of DNA alone raises the intriguing possibility of future discovery of other previously unsuspected species, hommin and otherwise.

Like Neanderthals, Denisovans left a genetic trace in modern humans. One example is the Denisovan gene variant that helps Tibetans live at high altitude. Additionally, the people native to New Guinea and other Pacific islands carry a substantial number of Demsovan sequences. Almost 5% of the genome of these people is of Demsovan origin. This finding suggests that Denisovans interbred with the ancestors of Pacific Islanders, either in mainland Asia before the islands were first cotonized by people, or later, if Denisovans were somehow able to get to multiple islands.