These days, it’s generally frowned upon when humans try to have sex with members of other species. That was not the case for our ancestors. This year, researchers showed that ancient humans hooked up with individuals of other Homo species — and that doesn’t just mean Neanderthals.

By now, it’s no secret that early Homo sapiens hooked up with Neanderthals, also known as Homo neanderthalensis. Some modern humans carry the consequences of those ancient trysts in their DNA. Genes linked to depression risk and cigarette addiction, for example, have been traced back to Neanderthal genes.

But as we explain in the video above, the Homo genus has many members — and hominins were not always as picky as they are today.

This is #24 on Inverse‘s list of the 25 Most WTF stories of 2018.

As Inverse reported in March, scientists publishing in Cell uncovered evidence that our modern human ancestors hooked up with yet another hominin group known as the Denisovans, who were either a different species of Homo altogether or a subspecies of Homo sapiens. (While scientists figure it out, they’re referred to by the temporary name “Homo sapiens, subspecies denisova.”) Denisovans and Neanderthals are thought to have split off from modern humans on the evolutionary tree some 600,000 to 744,000 years ago; they split from each other about 220,000 years after that.

Comparing 5,600 sequences of present-day humans from different countries to the DNA sequence contained in a Denisovan girl’s pinky finger found in a Siberian cave, the researchers noticed some notable overlaps and coincidences in geography.

They concluded that two separate Denisovan populations ran into and mated with each other, resulting in two groups of present-day humans who carry Denisovan DNA: East Asians and people from South Asia and Oceania. (Neanderthal genes tend to be carried by people of European and Asian descent.)

Watch the video below to find out how Neanderthal genes affect us today.

There will, no doubt, be even more evidence of inter-species hookups as scientists continue to compare our DNA with the genomes of hominins past. For now, one thing is clear: Our modern human ancestors were always down for a good time.

As 2018 draws to a close, Inverse is counting down the 25 stories that made us go WTF. Some are gross, some are amazing, and some are just, well, WTF. In our ranking from least to most WTF, this has been #25. Read the original article here.