Infanticide among animals is a widespread phenomenon. It has often been regarded as pathological or erroneous, suggesting that such behaviour decreases the individual and inclusive fitness of the infanticidal animals. However, recent studies (surveyed by Hrdy 1979, Polis 1981) have shown that infanticidal behaviour can evolve and be adaptive, benefiting the individuals responsible for the infanticide. Even parental infanticide, e.g. untimely abandonment of young, may be an advantageous reproductive tactic, as suggested for Ursus arctos by Tait (1980); in Mesocricetus auratus pup cannibalism “is an organized part of normal maternal behavior which allows an individual female to adjust her litter size in accord with her capacity to rear young” (Day and Galef 1977).
Neither survey addresses the question of what mothers of iteroparous (multiply breeding) and polytokous species (having several young per brood) should do with a brood containing exceptionally few young. We present two ways of assessing whether Accepting or Rejecting few young will maximize a mother's lifetime reproduction.