January 21, 2011

Happily, we continue to learn more about our human ancestral past. With every, mostly fragmentary, addition to the physical evidence, the picture changes. The mysteries, and the fascination, seem only to keep growing. A case in point is the recent discovery at Denisova Cave, in Siberia, of a finger bone, 50,000 years old. Scientists at the Max Planck Institute for Evolutionary Anthropology, based in Leipzig, Germany, have extracted the entire genome from the finger bone and found that it belongs to a previously unknown hominid they have called Denisovans. Researchers will need more skeletal samples before they can say what the Denisovans looked like. But they are believed to have emerged from Africa at roughly the same time as Neanderthals — 500,000 years ago — and settled much farther east. The scientists reached this conclusion by comparing Neanderthal and Denisovan genomes with the genomes of modern humans. In Nature last month, they reported that as much as 4.8 percent of Denisovan DNA turned up in the DNA of people living in Papua New Guinea and the nearby island of Bougainville. Given the distance between Siberia and Papua New Guinea, there’s every possibility the Denisovans were as successful and wide ranging as Neanderthals, who settled in Europe and the Near East. The story that needs updating in our minds isn’t just the existence of another hominid. It’s the fact that humans overlapped and interbred with both Neanderthals and with Denisovans. We carry the traces of these cousins in our genes. What is still unanswered is why we humans survived and prospered, while the Neanderthals and Denisovans disappeared. After all, Neanderthals and Denisovans had already prospered for 200,000 or 300,000 years by the time they faded away.