According to a study conducted by Omer Gokcumen, an assistant professor of biological sciences at the University of Buffalo, ancient humans had intercourse with a "ghost species" of "proto human".
Gokcumen explains that humans are only one member of a broader species named "hominins".
The research found that humans had sex with other members of the hominins group.
Gokcumen found "wildly different" genes in DNA of humans living in Sub-Saharan Africa. He believes these genes can be traced back to about 150,000 years ago when ancient humans were breeding with this mysterious "ghost species".
This other species is referred to by the scientific community as a "ghost species" as there are no known fossils that can be analysed.