User blog comment:D. Cello/Assassinews 10/11 -- Desmond's Ancestry Revealed/@comment-1884750-20111013230537/@comment-3310127-20111014024435

I meant in my previous comment, "Though every human held the potential for it, bloodlines of humans who interbred with Those Who Came Before held a greater concentration of the necessary genes, and were thus more likely to exhibit the ability."