Researchers have long recognized that a large surplus of young men can lead to social disorder, as happened on the frontier in 19th-century America. A counter theory, however, holds that a shortage of men can also be disruptive.
The theory comes from the late Marcia Guttentag of Harvard University and Paul Secord of the University of Houston. They explored the dynamics of marriage and partnership among the African-American community, which has the largest recorded shortage of men of any ethnic subgroup in the world. On purely demographic grounds, they concluded that a low sex ratio--the number of males per 100 females--may make men reluctant to marry or invest in children, particularly if their incomes were inadequate. If they did marry, they were at high risk for divorce or separation. Among the black population, many men could not find work--good-paying factory jobs in Northern cities began disappearing in the 1960s--and some turned to crime. These factors help to destabilize conventional family structure and result in births to unwed mothers, many of them teenagers, who tend to have limited skills in raising children. Their sons tend to be more crime-prone than sons of two-parent families.