Outbreeding is one possibility. There are now more people migrating than ever before, and over long distances. In the past most people stayed very close to wher

Outbreeding is one possibility. There are now more people migrating than ever before, and over long distances. In the past most people stayed very close to where they were born, which greatly increased the odds of inbreeding especially among lower classes. Today we have ubiquitous cheap transportation and more than 50% of the human population is now urban -- meaning bigger gene pools and lower odds of breeding between close relatives. http://en.wikipedia.org/wiki/Heterosis http://en.wikipedia.org/wiki/Heterosis http://en.wikipedia.org/wiki/Heterozygote_advantage http://en.wikipedia.org/wiki/Heterozygote_advantage I also must point out that "hard selection" (differential survival) is not the only operating mechanism in evolution. In complex organisms that reproduce sexually, it might not even be the dominant mechanism. You've got sexual selection and genetic drift, which in a species with low infant mortality and low mortality in general (a.k.a. us) are probably the dominant mechanisms. Beyond those you have things like the Baldwin effect, which get very interesting when coupled with epigenetics. Epigenetics is unquestionably real but as yet is not well understood. There could be all kinds of interesting things going on here. http://en.wikipedia.org/wiki/Baldwin_effect http://en.wikipedia.org/wiki/Baldwin_effect http://en.wikipedia.org/wiki/Epigenetics http://en.wikipedia.org/wiki/Epigenetics