Maternal Infanticide

Infanticide by mothers is a rare and counterintuitive event. Contrary to infanticide by individuals other than the mother (e.g. males wanting to reproduce with the mother or females wanting to get rid of competitors), the adaptive value of maternal infanticide is unclear. Among primates, it is most common in humans (an average of 34 cases a year in the US) and callitrichids. It might be one of the negative consequences of cooperative breeding, whereby a mother judges her infant as ‘undesirable’ and requiring a greater investment than the mother is willing or able to provide. Undesirability can simply be due to unfortunate timing rather than to any defects of the infant. In humans, for example, undesirable characteristics that have been linked to maternal infanticide/neglect have been sex, when one gender is favored over the other; presence of many older siblings; young age of the mother; poor health; or lack of paternal contribution to child care. In the few callitrichid examples available, maternal infanticide also seemed to be related to a scarcity of male helpers at a time when more than one female was breeding in the group. Maternal infanticide can thus be considered adaptive if the infant has low reproductive value or low survival chances, and if terminating investment in it increases either the mother’s future reproductive chances or her current investment in other offspring. In other apes, male infanticide is the most common and has been documented in particular after group takeovers in gorillas, and during aggressive inter-group encounters in chimpanzees. Female infanticide is less common, and is sometimes considered pathological or deviant behavior. Maternal infanticide is extremely rare in non-human primates.