Oh, they've gotten through a lot more than one round -- enough so that the odds of it not being due to external influence are driven well into the basement.Darwin is a statistical filter, not an absolute one. Your extant relatives got through one round but over the long haul, the filter will get them, or their progeny. That or the movie Idiocracy is a best estimator. Darwin will outlive democracy, the nanny state and us. The problem of course is we still have to put up with those relatives in the here and now. Bummer!
Idiocracy was a good demonstration of The Cash Register Syndrome and my personal belief that civilization is a self-defeating concept.