It's worth pointing out that men also tend to outnumber women significantly at the far left end of most bell curves. Data appears to show that for many traits, men have higher variability of traits, possibly caused by the differing sexual selection strategies of men and women. (There is much more diversity among mitochondrial DNA than Y-chromosomal DNA, which is just one piece of evidence among many that a smaller number of males produce a disproportionate amount of the offspring.)