A new, improved sequencing of ancient human relative genomes reveals that Homo sapiens didn't only have sex with Neanderthals and a little-understood line of humans called Denisovans. A fourth, mystery lineage of humans was in the mix, too.
As reported by the news arm of the journal Nature, new genetic evidence suggests that several hominids -- human relatives closer than humans' current living cousin, the chimpanzee -- interbred more than 30,000 years ago. This group of kissing cousins included an unknown human ancestor not yet revealed by the ancient DNA record.
"It's implied it could be something like Homo erectus or similar," said Carles Lalueza-Fox, a paleogenomics researcher at Pompeu Fabra University in Spain, who was not involved in the research, but who was present at a talk on the findings given by lead author David Reich of Harvard Medical School at a meeting on ancient DNA sponsored by the Royal Society in London on Nov. 18. Homo erectus is an extinct species of human that originated in India and spread into Asia. (See Images of Our Closest Human Ancestor)
Ancient human lineages
Neanderthals are an extinct group of humans who lived between about 30,000 and 130,000 years ago. Despite their reputation as bone-headed dummies, Neanderthals were likely as advanced as modern humans in areas such as tool-making, though they were probably less socially adept.
Denisovans are a far more mysterious group. These early humans lived in Siberia and probably split off from the branch of the human family tree that would eventually give rise to Neanderthals about 300,000 years ago. Little is known about how Denisovans lived and what they looked like.
But genetic analyses of Neanderthals, Denisovans and modern humans suggest the three groups occasionally had sex and produced offspring. Denisovan genes show up in modern Pacific Islanders and in people from Southeast Asia and southern China. Neanderthal genes appear in 1 to 4 percent of modern Eurasian people, suggesting that Homo sapiens and Neanderthals interbred after modern humans trekked out of Africa.
For unknown reasons, Homo sapiens are the only human survivors, as all others in the Homo genus eventually went extinct.