“Quite possibly, readers ten years from now may take for granted the occurrence of infanticide in various animal species,” Glenn Hausfater and I rashly conjectured back in 1984, in a preface to the first book on this subject, “and [they] may even be unaware of the controversies and occasionally heated debate that have marked the last decade of research on this topic…”. For biologists, that projection turned out to be more or less accurate. For those with backgrounds in the social sciences, perhaps especially in my own field of anthropology, it was wildly optimistic.

Most animal behaviorists now take for granted that the killing of infants by conspecifics can be found throughout the natural world and that, for many primate species, the arrival in their group of unrelated males represents a threat to infant survival. Many anthropologists, however, remain skeptical of the proposition that a propensity to attack infants born to unfamiliar females evolved in non-human primate males because it increased their chances to breed. This would require accepting that a behavior obviously detrimental to the survival of the group or even the species could evolve in males through Darwinian sexual selection because it provided the killers with a reproductive edge in their competition with rival males.