HUMANITY has a filthy secret: our ancestors used to have sex with members of other species.

That’s the finding in a new piece of research which suggests ancient people used to romp with a “ghost” species of proto human.

We are just one of a number of species known as hominins. Members of this family include Neanderthals and Denisovans, which are no longer found on Earth.

“It seems that interbreeding between different early hominin species is not the exception — it’s the norm,” said Omer Gokcumen, assistant professor of biological sciences at the University of Buffalo.

Gokcumen tested the DNA of humans living in Sub-Saharan Africa and found genes which were “wildly different from versions found in other modern humans”.

These genes probably trace back to prehistoric rumpy pumpy which probably took place about 150,000 years ago between our ancestors and a mysterious species.

“Based on our analysis, the most plausible explanation for this extreme variation is archaic introgression — the introduction of genetic material from a ‘ghost’ species of ancient hominins,” Gokcumen added.

“This unknown human relative could be a species that has been discovered, such as a subspecies of Homo erectus, or an undiscovered hominin.

“We call it a ‘ghost’ species because we don’t have the fossils.”

People living today would be a lot more like Neanderthals had it not been for a quirk of evolutionary fate.

This article originally appeared on The Sun.