A new study has found that Neanderthals interbred with modern humans about 100,000 years ago — far earlier than had been previously thought.

The study, which came from the Max Planck Institute for Evolutionary Anthropology and published in the journal Nature, indicates that residual DNA from Homo sapiens was found during the genetic analysis of the remains of a Neanderthal woman, indicating that the two species interbred 40,000 to 50,000 years earlier than scientists believed, according to a Fox News report.

It’s an astonishing find that turns current theories about when humans migrated out of Africa on its head, and shows that Neanderthals and modern humans interacted with each other a lot more often than most people assume.

Scientists are scratching their heads over where this interbred population came from and what happened to them, although there is one plausible theory about what happened. Scientists think that a small group of Homo sapiens may have left Africa and headed to parts of Eurasia, but they failed to set up a permanent colony. The Neanderthal remains were in Siberia near the border with Mongolia.

Neanderthals and modern man separated on the evolutionary tree about 600,000 years ago. Those who have Asian or European ancestry are believed to have about 2 percent of the DNA of Neanderthals.