Both the New York Times and the Washington Post have had pieces on the hypothesis that puberty now begins earlier than it used to. The NYT article, from March, is on girls, the more recent WaPo article on boys. Neither is able to give much data. I get the impression that research in this field is at its infancy, and that one aspect which limits it is lack of good data on puberty and its timing in the past.
The article on girls' earlier puberty states that the age of menarche (the onset of menstruation) does not seem to have changed much, if at all, but that secondary sexual characteristics (breast development and body hair) may now appear earlier.
What this means seems to be debated. One researcher argues that these developments might not have anything to do with puberty:
Adding to the anxiety is the fact that we know so little about how early puberty works. A few researchers, including Robert Lustig, of Benioff Children’s Hospital, are beginning to wonder if many of those girls with early breast growth are in puberty at all. Lustig is a man prone to big, inflammatory ideas. (He believes that sugar is a poison, as he has argued in this magazine.) To make the case that some girls with early breast growth may not be in puberty, he starts with basic science. True puberty starts in the brain, he explains, with the production of gonadotropin-releasing hormone, or GnRH. “There is no puberty without GnRH,” Lustig told me. GnRH is like the ball that rolls down the ramp that knocks over the book that flips the stereo switch. Specifically, GnRH trips the pituitary, which signals the ovaries. The ovaries then produce estrogen, and the estrogen causes the breasts to grow. But as Lustig points out, the estrogen that is causing that growth in young girls may have a different origin. It may come from the girls’ fat tissue (postmenopausal women produce estrogen in their fat tissue) or from an environmental source. “And if that estrogen didn’t start with GnRH, it’s not puberty, end of story,” Lustig says. “Breast development doesn’t automatically mean early puberty. It might, but it doesn’t have to.” Don’t even get him started on the relationship between pubic-hair growth and puberty. “Any paper linking pubic hair with early puberty is garbage. Gar-bage. Pubic hair just means androgens, or male hormones. The first sign of puberty in girls is estrogen. Androgen is not even on the menu.”Several theories exist on the possible causes of earlier puberty in girls, assuming that it indeed is earlier, and more research is clearly needed.
The NYT article is titled "Puberty Before Age 10: A New ‘Normal’?." That misleads in two ways: the article is only on girls, not on boys, and given that the average age of menarche has (perhaps*) fallen only from 12.8 to 12.5 years since the 1970s the more correct title would have replaced the word "puberty" with "the beginning of female puberty." Yeah, that's clunky and yeah, I know that the authors of articles mostly don't have a say with the titles the newspapers pick.
The WaPo piece, on boys, is even more anecdotal in its approach (though I'm not blaming the authors of either piece for the current state of knowledge in the field). An example:
For 800 years, the St. Thomas Boys Choir has been filling churches with pure, young voices. Now it’s confronting a confounding phenomenon: Every year, those voices are cracking with teenage angst just a little earlier than before.The topic of earlier puberty clearly calls for a large study, given both the possible health and social consequences. The latter are described in the article on girls though mostly as they apply to girls who develop earlier than average. The consequences might be different if the whole age range of puberty shifts downwards for all children.
Other boys choirs have been noticing it, too, as an unrelenting march of puberty sweeps voices into rebellion. Over recent decades, the already-short careers of their sopranos have started to end between six months and a year earlier, challenging them at times such as Easter, for which choral music such as J.S. Bach’s St. Matthew Passion was written with difficult lines for boys free of hormonal woes.
At the venerable St. Thomas Boys Choir, where Bach once drilled pupils in their scales, leaders have redoubled recruitment efforts and taken in boys at a younger age to make sure the choir has a full stock of voices ranging from the deepest bass to the most clarion-pure soprano. Children whose voices are deepening wait out the change by working the ticket booth.
The cause of the shift remains unclear.
*I added this qualifier for two reasons: First, I'm not sure how good historical data is on the onset of puberty, given that routine physician or school nurse records of that would probably be pretty incomplete and not representative in the past. We have more data today.
Second, if different ethnic or racial groups experience menarche at somewhat different average ages, then the change could be caused by a different mix of individuals in the population rather than by a drop in the overall average age at menarche.