And if so, what is the cause?

Ryan discusses the popular belief that something in our food or environment might be at fault:

Just a thought, since you've been blogging on the organic trend; There have been claims that women today have earlier onset of menstruation than they did fifty-some years because of hormones in foods and the environment.

It seems to me that several other factors, including better nutrition and also a changing racial demographic could better explain this fact. African-American women are shown to start menstruation over a year earlier than caucasians, and their percentage of the population has increased over the past 50 years.

I still buy organic milk when I buy the stuff. However this seeming misinterpretation of data has always bothered me. I can go through and give some support via links after I get off work if anyone is interested.

First, are girls going through puberty earlier? I'm inclined to think so. When I was in school, it seems that most girls were developing breasts in "middle school" -- some as early as the 5th or 6th grade, most by 7th or 9th. And, if I'm not mistaken, written records of earlier times seem to indicate an even later age of development. Now, the ever-present "studies" (like this one) are assuring us it is entirely "normal" (when do we get to use that word?) for girls to develop breasts in the second grade.

Next: If so, why?

I am inclined to give the body-weight hypothesis some credence: I know girls who were deeply into gymnastics, slightly anorexic, and skinny as a rail. Some of them didn't develop breasts until quite late in their teen years. But I think that works in terms of slowing down development, and I don't think such an effect accounts for the massive shift I think we're seeing in onset age.

Some groups reflexively suggest every possible technological development is at fault: insecticides, growth hormones, plastics. Though I myself once tended to (equally reflexively) echo such suspicions, I'm now learning that such speculation isn't driven by data, but by the same psychology which led Don Quixote to joust windmills: fear of progress. (Ironic, considering such now often comes from people who insist we call them "progressives".)

(That isn't to say they're wrong in every case: Surely, in some cases, there will be a few such effects. But the claims consistently outnumber and overreach the evidence.)

Are we using or ingesting a lot more or worse insecticides than in the 1960s, when girls allegedly "developed" later? Are chemicals associated with plastics leeching into our water, food, and bodies? Do they have a hormone-like effect on us? I haven't seen any hard data to that effect, though I've heard many claims.

(To the contrary, the big smoking gun many argued was evidence of this -- deformed frogs -- was recently shown to simply be caused by a parasite. Plain old nitrogen -- which is even found in the fertilizers used by organic farmers -- was found to be the key environmental factor. Atrazine might be implicated in subtler effects on frog sexuality -- or not, depending on who you ask -- but the data is far from conclusive. And again, some European countries have banned atrazine -- but I would doubt they show significant puberty-age differences.)

I suspect we're still prone to a lot of "homeopathic" thinking -- that is, that like must cause like. If I eat fat, it must make me fat. (Never mind the carbs!) If I drink milk which I think has hormones in it, it must make make something hormonal happen. (Never mind that vat of hydrochloric acid en route! And never mind studies showing no difference in concentration.)

(By the way, I also buy organic milk, but simply because its ultrapasteurized, and thus has a longer shelf life.)

Yet Europe, if I'm not mistaken, has banned hormones like BST. So why are European girls also experiencing puberty early? And how about the children of health-food consuming people? Just a guess, but I don't think you'll see a difference there. So I suspect we have to look elsewhere for an answer.

One idea which intrigues me -- one which I think a lot of people might reject -- is that there's a lot stronger brain/body link between a girl's social context and her hormones than we might have previously suspected.

For example (again, this is just a guess), it may be that when a girl is exposed to a sexualized environment, with lots of thoughts or discussions of procreative acts, that her body somehow prepares for such. Certainly, that would be a very useful ability in more primitive times.

And it would appear that this idea isn't entirely out on a limb. According to a study cited in ScienceDaily:

The study looked at 173 girls and their families from Nashville and Knoxville, Tenn. and Bloomington, Ind. from the time the girls were in pre-kindergarten until they were in the seventh grade.

Girls who had close, positive relationships with their parents during the first five years of life tended to experience relatively late puberty, compared to girls who had more distant relationships with their parents. More specifically, the researchers found that the quality of fathers' involvement with daughters was the most important feature of the early family environment in relation to the timing of the daughters' puberty.

Girls who enter puberty later generally had fathers who were active participants in care-giving; had fathers who were supportive to the girls' mothers; and had positive relationships with their mothers. But it's the fathers' involvement, rather than the mothers', which seems to be paramount to the age of the girls' development. The researchers believe that girls have evolved to experience early socialization, with their "antennae" tuned to the fathers' role in the family (both in terms of father-daughter and father-mother relationships) and that girls may unconsciously adjust their timing of puberty based on their fathers' behavior.

I suspect the link is slightly less direct: that girls who have close fathers won't be mentally seeking an affirming "father love" through sexual acts, and thus that they won't be thinking about or as responsive to sexual thoughts and opportunities. And indeed, the same factor -- a caring father -- also correlates strongly with the time at which girls become sexually active, and the frequency of such activity. (Other theories are mentioned in the article.)

This seems to be a rather powerful explanatory model. Why do black girls have puberty a year earlier, on average, than white girls? The higher rate of fatherless homes in the black community then comes into consideration. Why are girls going through puberty earlier than before? Again, the break-up of the nuclear family correlates strongly with this trend.

I'm not saying it explains everything or that there are no other factors (indeed, I think weight and physical activity also play a role), but I don't think most people are considering this -- I suspect many may have strong reasons not to consider it, since would lead to an altogether different set of social policies and values than some might prefer.