The greater the precision of female reproductive synchrony—the greater the number of ovulating females who must be guarded simultaneously—the harder it is for any dominant male to succeed in monopolising a harem all to himself. This is simply because, by attending to any one fertile female, the male unavoidably leaves the others at liberty to mate with his rivals. The outcome is to distribute paternity more widely across the total male population, reducing paternity skew (figures a, b).
The greater the precision of female reproductive synchrony—the more females are fertile at the same time—the harder it is for a dominant male to control all the females in his harem. This leads to a wider distribution of paternity across the male population, reducing the dominance of any single male.