Hybridization is correct, I believe. Is it possible that the negatives are the descendants of the Watcher angels that bred with daughters of man to create the "Nephelim" race of the Bible? Are the Red Headed Giants (that TPTB have kept secret through this century) and the Nordic Vikings possibly decedents of the Nephelim then??

Either way, it's a mute point since realistically, Rhesus Negatives are going extinct in a few more generations.
No more gingers....