The Three Sirens — Irving Wallace

A team of 9 oddly assorted Americans, led by Dr. Maud Hyden, a world-famous American anthropologist, goes to a remote Polynesian island for 6 weeks with the purpose of facing uninhibited behavior and customs.

They find a society where the monotony of marriage is relieved by the freedom to enjoy other mates one week of the year; where the dissatisfactions and repressions of men and women are relieved in a mysterious Social Aid Hut, where women over 40 can enjoy life; where unattractive girls are desired; where grown men do not have to prove their virility by means of their careers.