"The first choice of object in mankind," Freud believed, "is regularly an incestuous one." Sir James Frazer, the British anthropologist, also explained the almost universal ban on incest as a necessary safeguard against man's urge to mate with the most available partner: "The law only forbids men to do what their instincts incline them to do." For years, most scientists discounted a contrary suggestion by Finnish Anthropologist Edward Westermarck that close childhood association discourages erotic feeling.
More recently, Westermarck's theory has been gaining ground. Observation of kibbutz life in Israel indicates that the...