I analyse and summarize the empirical evidence in mammals supporting a
lternative benefits that individuals may accrue when committing nonpar
ental infanticide. Nonparental infanticide may provide the perpetrator
with nutritional benefits, increased access to limited resources, inc
reased reproductive opportunities, or it may prevent misdirecting pare
ntal care to unrelated offspring. The possibility that infanticide is
either a neutral or maladaptive behaviour also is considered. I devote
the second half of this article to reviewing potential mechanisms tha
t individuals may use to prevent infanticide. These counterstrategies
include the early termination of pregnancy, direct aggression by the m
other against intruders, the formation of coalitions for group defence
, the avoidance of infanticidal conspecifics, female promiscuity, and
territoriality. I evaluate the support for each benefit and counterstr
ategy across different groups of mammals and make suggestions for futu
re research.