Why Mothers Do Not Resist Infanticide: a Cost-benefit Genetic Model.

Infanticide has recently been observed in several primate species while female counterstrategies are seemingly rare. The question of why mothers do not increase their resistance to infanticide is investigated using a haploid two-locus model. A hypothesis that mothers can recover lost offspring by gaining more grandchildren is rejected in most cases, and it is shown that costs and benefits for both males and females have the strongest influence on the evolution of infanticide and obedience to it. An estimation of parameters for a natural population of hanuman langurs suggests that infanticide is more advantageous than noninfanticide and the costs of resistance, compared to obedience, is higher than its benefits. Data from other studies on primate infanticide are discussed in the light of results of the model.