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Male mammals often kill conspecific offspring. The benefits of such infanticide to males, and its costs to females, probably vary across mammalian social and mating systems. We used comparative analyses to show that infanticide primarily evolves in social mammals in which reproduction is monopolized by a minority of males. It has not promoted social counterstrategies such as female gregariousness, pair living, or changes in group size and sex ratio, but is successfully prevented by female sexual promiscuity, a paternity dilution strategy. These findings indicate that infanticide is a consequence, rather than a cause, of contrasts in mammalian social systems affecting the intensity of sexual conflict.
Why some male animals kill infants
One of the most unpleasant aspects of social life in some animal species is killing of the young by adult males. Lukas and Huchard looked at mammalian groups with a variety of social systems—from mice to mongoose and from bats to bears. Infanticidal behavior in males appeared to be a result of sexual conflict in social species with nonseasonal breeding. Killing of a female's young by a new male will speed her return to a reproductive state and allow him to raise his own young. Evolutionarily, the only successful defense in females appears to be polyandry: Females that mate with multiple males make it hard for any one male to know that he is, or is not, the father of her offspring.
Science, this issue p. 841