Reconstruction of Homo erectus – a candidate for the mystery hominin that had sex with the ancestor of Neanderthals and Denisovans P.PLAILLY/E.DAYNES/SPL

It is the oldest and one of the most extreme case of interbreeding found so far in the tangled tale of human origins. Around 700,000 years ago, a group of ancient humans that would later give rise to both the Neanderthals and Denisovans mated with an unidentified group of hominins.

This mystery group had evolved separately from their new sexual partners for over a million years. Despite this, the two groups were able to interbreed – although the …