These days, however, it's getting harder than ever for choirmasters to fill those top spots. Boys' earlier puberty times may have escaped notice a bit longer than girls' because boys' first signs aren't as obvious as girls' budding breasts and first periods, NPR reported in December 2012. But now a growing number of studies have noticed the male trend. Last year, a study published in the journal Pediatrics found a representative sample of U.S. boys entered puberty about a year and a half earlier than boys studied in the U.K. 40 years ago. The New York Times Magazine cited research from a University of California, Berkeley, demographer, which shows the age of puberty for boys has inched forward 2.5 months every 10 years since the 1700s. This latter research is more relevant to boys choirs, but it's a bit more uncertain, as records of puberty timing don't exist for boys 100 years ago or more, so it must use an indirect method of estimating 18th-century pubescence.