John Money's clinical concepts of sexual/erotic gender development and pathology (1980, 1993) may also shed some light on why sons and mothers, separated early in the child's development, become sexually drawn to each other in later years, when not aware of their kinship ties. He points out that male/female image reciprocity is a criterion of lovemap matching, and that the formation of male and female lovemaps is dependent on input from the social environment, from the time of birth to puberty. This postnatal social input is often greatly influenced by maternal-child interactions. The template that ensues, may, in some cases, carry a heavy attraction to the parent of the opposite gender.