Many cultures consider large age differences between men and women in romantic relationships acceptable. Western culture has traditionally encouraged relationships between young women and older men for two reasons. First, older men often have more financial resources and are better providers than younger men. Second, young women are more likely to produce healthy children than older women.

Many social commentators have argued that this trend encourages adult men to form sexual relationships with underage girls and increase their risk of pregnancy. According to author Linda Villarosa, “67 percent of teenage mothers are impregnated by men who are over twenty years old. . . . Whether coerced or voluntary, couplings between teenage girls and adult males are many times more likely to result in pregnancy than teen-teen sex.” Villarosa and others maintain that “predatory” adult males pursue young girls and contribute to...