Seals and Group Selection

Seals have been shown to restrict recruitment in crowded populations because of gregarious and hierarchical behavior. Some authors have suggested that such behavior has evolved through group selection to prevent overutilization of resources. Published data are reviewed to show that more highly social seals have higher potential rates of increase. This is difficult to reconcile with group selection, but easily explained in ordinary evolutionary terms. Females of social breeders have little choice of breeding sites, exercise little intelligence, and mature rapidly. Solitary breeders benefit from accumulated knowledged of the environment, produce young more successfully when older, and therefore mature slowly. Species with lowest potential rates of increase breed biennially at most, because they give their young extended periods of parental care. Deferred maturity, fatal crushing of newborn young, and other restrictions of recruitment in crowded populations of polygynous species can be explained as excesses of sexual selection. There is no necessity for postulating group selection in the evolution of seals.