Introduction

The sexual selection hypothesis for the selective advantages of infanticide by males requires that certain conditions be met. Provided the male is able to locate the infant, in order to derive reproductive benefits from infanticide he must be able to kill it with limited costs, the female must resume ovarian cycling earlier or produce more offspring than she would do otherwise, and he must gain mating access to the female when she resumes cycling (Hrdy 1979; van Schaik, Chapter 2). Whether or not these conditions are met depends on life style and life history. Life style variables are the location of the infants relative to the female, the presence or absence of hiding places for infants, and the degree of predictability of female spatial position in territories. Life history variables include the degree of infant precociality, and hence their ability to escape from attacking males, and the speed of female reproduction, i.e., their ability to be pregnant and lactating at the same time.

In this chapter, I examine whether infanticide by males is concentrated in species with the expected female life history. Infanticide by males is most advantageous where lactation is long relative to gestation. In such species, postpartum mating and early pregnancy are impossible because this would produce two sets of young of different ages, different needs and different competitive power for access to milk.