Categories of unfamiliar semen One simple algorithm that may have evolved to solve the adaptive problem posed by both the mother’s and infant’s need for a caring, committed adult male would be a mechanism that could distinguish between familiar and unfamiliar semen. Frequent insemination of a female by the same male over an extended period of time would be a relatively good biochemical index of the existence of a committed pair bond and, therefore, semen familiarity would predict the likelihood of long-term provisioning, protection, and care of the mother and the child during pregnancy and following parturition.