One intriguing paradox of reproduction is that women are having babies later but preparing for it earlier. The age of first menstruation for women has fallen from fifteen in the late nineteenth century to just twelve and a half today, at least in the West. That is almost certainly because of improved nutrition. But what cannot be explained is that the rate has accelerated even further in more recent years. Just since 1980, the age of puberty has fallen in America by eighteen months. About 15 percent of girls now begin puberty by age seven. That could be a reason for alarm. According to the
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