(Photo: Paul Hudson/CC BY 2.0)

Tens of thousands of years ago, Neanderthals—our ancestors—roamed the earth.

But they weren’t our only ancient relatives, of course. Several species can stake that claim and, in 2008, a new one was discovered: Denisovans, so named for the Russian cave where scientists found one of their bone fragments. 

New research suggests that the Denisovans, Neanderthals, Homo sapiens and other early humans—thought to have lived separately—likely crossed paths. They probably also had sex. Or at least that’s what DNA evidence published in Science indicates. 

“Different populations of people have slightly different levels of Neanderthal ancestry, which likely means that humans repeatedly ran into Neanderthals as they spread across Europe,” a co-author of the study, Svante Paabo, tells NBC News.

How all of that prehistoric sex occurred is anyone’s guess, but it seems to have happened on multiple occasions. ”It was apparently separate events, so not just one single happy party at some point,” biologist Alan Cooper tells Science

These multi-species sex parties ended about 40,000 years ago, when Neanderthals became extinct and Homo sapiens began spreading in earnest across Europe and Asia. But Neanderthals are still with us—their name is now used as an ill-considered insult aimed at boorish humans.