Heightened attention Height is largely determined by genetics. Big people generally come from big parents, though advances in nutrition may also play a role in the apparent increase in the number of unusually tall athletes. Since the average height of American men has been trending upward throughout the past century, it stands to reason that there would be more tall athletes in every sport, but that is not enough to explain the dynamic increase in baseball. If it were totally a matter of evolution, the process presumably would take place at a much slower rate. It appears, in this case, that the Darwinian notion of natural selection has been replaced with just plain selection.
Baseball players are taller because scouts are out looking for taller baseball players.
When you go to the Dominican Republic, for instance, you get all these kids at the tryouts. The first thing you look at is how a guy looks in the uniform. You're very unlikely to give any money to a guy who's 5-9 and 170 pounds. The average 1960s kid played Little League and maybe Pop Warner football. The 1980s kid also had soccer, basketball and other team and individual sports to keep them active year-round.