I analyse and summarize the empirical evidence in mammals supporting alternative benefits that individualsmay accrue when committing nonparental infanticide. Nonparental infanticide may provide the perpetratorwith nutritional benefits, increased access to limited resources, increased reproductive opportunities, or itmay prevent misdirecting parental care to unrelated offspring. The possibility that infanticide is either aneutral or maladaptive behaviour also is considered. I devote the second half of this article to reviewingpotential mechanisms that individuals may use to prevent infanticide. These counterstrategies include theearly termination of pregnancy, direct aggression by the mother against intruders, the formation of coalitionsfor group defence, the avoidance of infanticidal conspecifics, female promiscuity, and territoriality. I evaluatethe support for each benefit and counterstrategy across different groups of mammals and make suggestionsfor future research.
