DNA from toe fossil reveals interbreeding among ancient species

A 50,000-year-old toe bone found in a Siberian cave is giving scientists a surprising view of the breeding habits of early humans.

In what has been described as a “Lord of the Rings”-type world, researchers say that Homo sapiens, Neanderthals and two other groups of early humans mingled and interbred thousands of years before all species but ours became extinct.

The findings were presented Wednesday in the journal Nature by a team of scientists who sequenced the DNA from the Neanderthal toe fossil and compared it to the genomes of 25 present-day humans, as well as the genome of a sister group to Neanderthals called Denisovans.

According to their analysis, Neanderthals contributed roughly 2 percent of their DNA to modern people outside Africa and half a percent to Denisovans, who contributed 0.2 percent of their DNA to Asian and Native American people.

The biggest surprise, though, was the finding that a fourth hominin contributed roughly 6 percent of the DNA in the Denisovan genome. The identity of this DNA donor remains a mystery.

Geneticists and anthropologists said the inch-long bone and resulting analysis have greatly illuminated a period of time roughly 12,000 to 126,000 years ago.