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 more precisely synchronized the ovulation cycles of female animals are, the harder it becomes for a dominant male to keep all females in his harem exclusively for himself. This is because, by focusing on one fertile female, he inadvertently allows other males to mate with her and spread paternity among the population.