If you think about it, kissing is a bit strange. That said, we’ve done it forever — and other species, like chimpanzees, bonobos and orangutans have all been observed kissing in the wild.

It turns out, this practice is *really* old. A new study found that kissing evolved in a common ancestor of humans and other great apes around 21 million years ago.

But it doesn’t stop there. This study and others also found that, way back when, interspecies kissing between humans and adjacent species was fairly common. For example, there’s strong evidence that humans and Neanderthals not only interbred, but kissed while they did it.

What does this mean for science? I have no idea, but if you ever wondered whether your ancient ancestor ever considered making out with a monkey, the answer is probably “yes.”