Sexual selection theory states that males compete for mate
monopolization and larger males can sire more offspring than smaller
males, thereby resulting in the evolution of sexual size dimorphism.
Female grouping facilitates mate monopolization and increases intensity
of sexual selection. Sexual selection should be particularly intense in
mammals because females have the most parental investment due to
gestation and lactation, making them a limiting resource for which males
compete. Nevertheless, I found evidence suggesting a minor role of
sexual selection in mammals. I found low values of the standardised
variances in male reproductive success, Im, and Nonacs’s B indices.
Phylogenetic confirmatory path analyses indicated that sexual dimorphism
evolved after the evolution of large body size, regardless of the
evolution of polygyny and breeding groups. Results are explained by a
‘gender neutral’ model, in which all individuals in a population are
initially subjected to the same pressures of natural selection.