>>54
Humans have risen to a state that we're are no longer effected by natural selection. For most of our history, this has left us stagnant. Within the last 100 years or so though, technological advances (especially medical) have kept alive genetically weak people alive. In my opinion, this plays a large role (along with pollution and other factors) in rising disease rates.
Another byproduct of the industrial & technological revolutions is the white-collar worker. Educated, intelligent people who use their minds, not their bodies to earn their wage. Generally these upper-middle class people have very few children. Compared to poorer working class families, who tend to have much larger families. Humanity is slowly become genetically weaker and weaker.