Greater male variableness is a result of only-males having a Y-chromosome. The function of the Y is to create more variation in males and hence speed evolution. Without the Y, evolution would proceed only by favorable mutations. Since females are the reproduction bottleneck, their genome has to be stable. Variation through mutation of the Y can produce a large number of unfavorable mutations and still have no effect on reproduction rates. In short, males mutate and females pick the winners. Sex was natures invention to speed up evolution. Sure the math is interesting but the underlying cause is more interesting to me.