In the 1970s, a Harvard psychologist proposed that the ratio of men to women shapes culture and politics. Her theory predicts U.S. social trends for the next 25 years.
When the sex ratio is low (too many women), women are more slender; when women are in short supply, as was the case in the United States in the 1950s, women are more curvaceous, perhaps because they are trying to look the part of traditional wife and mother. Barber’s studies, which often look at patterns in 40 countries or more, have shown the power of the sex ratio in predicting such things as the rate of nonmarital births, the practice of polygyny, and even the likelihood that men will grow facial hair. The more men there are, he found, the more hair they grow to attract mates.
When there is an excess of available men—as was true during most of U.S. history because most immigrants are male—marriage is generally revered and values are conservative. When available women outnumber available men, women are set free of the home, and values shift toward liberalism. But a low sex ratio also lowers the living standards of women and causes turmoil in relationships, mainly because men typically have more power in society, which they tend to exercise crudely when there are extra women around.