Ancient humans interbred with Neanderthals, Denisovans and a mystery species that may have originated in Africa and migrated to Asia, paleontologists said this week.

Improved genome sequencing from two extinct human relatives suggests the forerunners to modern humans intermingled with one another more extensively than was previously known.

Ancient genomes, one from a Neanderthal and one from a different archaic human group, the Denisovans, were presented Monday at the Royal Society in London, where researchers said they’d found evidence to suggest rampant interbreeding among members of ancient human-like groups more than 30,000 years ago in Europe and Asia – including an unknown human ancestor.

“What it begins to suggest is that we’re looking at a ‘Lord of the Rings’-type world -- that there were many hominid populations,” said Mark Thomas, evolutionary geneticist at University College London.

Previous Neanderthal and Denisovan genome sequences showed the two groups had interbred with anatomically modern humans, contributing to the genetic diversity of modern humans, and revolutionized the study of ancient human history.

But those genome sequences were of low quality and full of gaps and errors.

A team led by David Reich, an evolutionary geneticist at Harvard Medical School in Boston, Massachusetts, and Svante Pääbo at the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany, said they’d produced genome sequences that matched the quality of modern human genomes.

All humans whose ancestry originates outside Africa have about 2 percent Neanderthal genomes, and some Oceanic humans, such as Papua New Guineans and Australian Aboriginals, have about 4 percent of their DNA from interbreeding between their human ancestors and Denisovans, whose remains were found in a cave in Siberia’s Altai Mountains.

Researchers said the Denisovans interbred with Neanderthals and humans who lived in China, East Asia and Oceania.

But researchers said the new genomes also suggested that Denisovans interbred with another extinct population of ancient humans who lived in Asia more than 30,000 years ago, and scientists are left guessing who they might have been.

“We don’t have the faintest idea,” says Chris Stringer, a paleoanthropologist at the London Natural History Museum.

Stringer speculated that they might be related to Homo heidelbergensis, a species that left Africa about 500,000 years ago and later gave rise to Neanderthals in Europe.

“Perhaps it lived on in Asia as well,” Stringer said.

[Image via Agence France-Presse]