Medicine is rapidly finding cures for diseases that afflict us. Predators no longer stalk us. Our next meal is down the street at the grocery store. Moreover, nearly everyone is able to reproduce. A quick look at the Jerry Springer show indicates that even the most unattractive, unintelligent, immoral specimen of humanity is able to pass on his or her genes to the next generation.
Genetic drift is no longer an issue either.
As our population has boomed and the birthrate per individual declined, the possibility of one gene gaining superiority over others simply by chance is all but eliminated. Drift is effective only in small communities, but the global village precludes this. Even mutation is not a problem. We are able to detect detrimental mutations and eliminate them quickly. When they cannot be quickly removed from the genetic pool, science creates accommodations for them, nullifying any benefit or detriment that may have resulted.