If there is a genetically transferred trait that results in enough people with that trait breeding more than others without it then it will get selected for and ultimately become prevalent in the population.
The question here is whether or not modern technology and man's interference in natural processes mean that such a trait can emerge and flourish in this way. Things like AIDS resistance are certainly conceivably able to evolve in the human species in this manner I would have thought?
Perhaps more interestingly is whether or not we will develop the technology to manipulate our own genes such that we can bear children with the traits we want them to have. How this could play out and what the wider implications are is maybe not the sort of thing you were intending to discuss here........
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