I'd like to posit a hypothetical cause of the difference in bell curve spreads between males and females in any given area. Consider that, generally speaking, men are far less selective about their mates than women are. As a result, almost all women are capable of reproducing. Conversely, a male's reproductive potential is closely tied to his genetic desirability, (which in turn is connected inexorably with cultural norms and mores,) leading to the increased emergence of a plethora of exaggerated traits, including height. (Just an idea.) :)