source competition. Evidence supporting the idea that indi-
viduals commit infanticide to avoid misdirecting parental
care to unrelated offspring among rodents is rather limited.
The sexual selection hypothesis in which males kill infants
they have not sired as a means of reproducing with the
victims’ mother remains unproven in rodents; studies that
measure fitness benefits in terms of increased mating oppor-
tunities or of a reduced latency for the females to bear off-
spring of infanticidal males under wild or more seminatural
conditions are strongly needed. The nature of the mecha-
nisms by which parents prevent infanticide has been con-
troversial, and future studies need to consider two critical
issues. First, information is needed from animals whose be-
havior is recorded under realistic ecological conditions. Sec-
ond, alternative hypothesis should be stated a priori: the be-
haviors that have been suggested to be counterstrategies in
rodents have other hypothesized functions as well. Overall,
we encourage future investigators to design studies that will
simultaneously evaluate multiple functional hypotheses and
their specific predictions.Nonparental Infanticide 279