We don't know much about our most recent relatives. Our only evidence that they ever existed is a finger bone fragment and two teeth. But now new genome data shows that they were not only related to us but also to our more distant relatives, the Neandertals.
Called Denisovans (after the Denisov Cave in Siberia where the fossils were found in 2010), these relatives may have lived about 800,000 years ago until they disappeared about 30,000 years ago. Matthias Meyer and Svante Paabo of the Max Planck Institute for Evolutionary Anthropology in Leipzig, and their colleagues announced their genome sequencing findings in the August 30 issue of Science.
By sequencing the genes from the bone fragment, the researchers found that the bone belonged to a young girl who lived between 74,000 and 82,000 years ago. By comparing the Denisovan girl's genome with that of Neandertals and 11 modern humans, they discovered that modern Papuans and Melanesians share a significant number of genes with the Denisovans. The results show that the Denisovans are a distinct line of ancient humans and while not Neandertals, they were more closely related to Neandertals than to most of us. The findings also show that the Denisovans lived over a huge area of the world, and experienced very few genetic variations during their existence.
"Genetic variation in Denisovans was lower than in present-day humans," Mayer said. "This is likely due to the fact that an initially small Denisovan population grew quickly while spreading over a wide geographic range."
Part of that range included Southeast Asia, New Guinea and Australia. The researchers estimated that about 6.0 percent of the genomes in modern Papuans come from ancient Denisovans. These ancient people may also have contributed to the genomes of Melanesians, Australian Aborigines and islanders in what is now the Philippines. In fact, many traits among these groups--dark skin, brown hair and eyes--were also traits of Denisovans.
The findings also showed that while Denisovans were closely related to us, we may not have been able to have a conversation. Since humans split from the Denisovans, about 100,000 changes in the human genome have occurred, the researchers said. Those changes affected brain function and nervous system development, include two genes associated with autism and language disorders. These results imply that fully developed language developed only in modern humans. "This work will help determine how modern humans came to expand dramatically in size and in cultural complexity, while archaic humans eventually dwindled in numbers and became extinct," said Paabo.