So that's what King Kong was wanting to do with the blonde!
Decode's alternative proposal is that the flipped version was carried for many years in a different human lineage, one of the archaic populations that preceded the emergence of anatomically modern humans in Africa 150,000 years ago. Then, in some episode of rape or interbreeding, a single copy of the flipped version entered the modern human lineage some time before humans left Africa 60,000 years ago.
...and it sounds like he gaver her lice too. This is exactly the kind of thing your mother warned you about.