Revisiting Infanticide in Non-Human Primates Reveals a Similar Likelihood of Male and Female Perpetrators

Infanticide is understood as any direct or indirect behavior that fatally harms an infant, regardless of whether the perpetrator gains benefits. In non-human primates, males are frequently identified as the perpetrators. Classical studies categorized behaviors like "abuse", "fatal neglect", "kidnapping", and "aunting to death" as forms of infanticide when they resulted in infant death. However, in more recent literature, some of these behaviors are excluded from classifications of infanticide without clear justification, particularly those involving female-related lethal actions. Therefore, we conducted a systematic review spanning 54 years to investigate potential sex biases in primate infanticide literature. Our findings show that female actions leading to infant death are often labeled with terms like "abuse" and "fatal neglect". In contrast, similar male behaviors are consistently classified as infanticide. As a result, infanticide by non-human primate females has been systematically underreported. Classifying all lethal behaviors by females toward infants as infanticide eliminates the sex difference in the frequency of such acts. Our study shows that being consistent with the original definition of infanticide for non-human primates provides a more accurate understanding of infanticide in these animals. Thus, we strongly recommend adhering to the infanticide definition, which integrates the recorded behaviors into established theoretical frameworks, enabling more comprehensive discussions of primate infanticidal behavior.