The distribution of most human traits can be represented by a bell curve, where the two ends of the curve represent the extreme occurrences of a particular trait, and the summit of the curve represents the mean between the extremes.
Take, for example, the distribution of height in the adult male. We would expect the far-left potion of the curve for this trait to indicate a relative infrequency of small-statured males; the far-right portion to indicate a relative infrequency of large-statured males. Visually, it would be easy to see that the proportion of adult males who are either extremely small-statured or extremely large-statured is relatively small. A similar curve would apply, presumably, to male aggressiveness, with a small percentage of males manifesting as Ferdinand the Bulls; an equally small percentage manifesting as Attila the Huns. In fact, aren’t such relative extremes central to our survival over millennia? Isn’t it at the extremes of any particular trait, in fact, where nature tinkers most boldly toward building a better mousetrap? And aren’t we all, our race as a whole, the result of this bold tinkering? To the tinkerers goes the future?