I’ve seen a study which found that the age of puberty (especially female puberty) is dropping rapidly. In 1860 it started around 16.8 and in 2010 it was 10.8. Why is that? Is there any explanation?
In: Biology
Pubertal timing is mostly explained by body fat percentage by mass. Once you hit about 10% fat by mass, the arcuate nucleus in your hypothalamus will start doing its job to trigger the onset of puberty.
We see later puberty a hundred years ago because, on average, girls took longer to hit that 10% body fat because food was more scarce. This was the case throughout most of human history. Similarly, elite athletes are often under 10% body fat, so it takes them longer to hit menarche, too.
We are seeing age at pubertal onset dropping partly because of better health. We are heavier because we aren’t starving, which is a good thing. On the other hand, it’s also about poor health and the obesity epidemic, causing girls to hit 10% by the time they’re 7 or 8.
The way to view puberty in girls is to consider what it means. Your body is finely tuned to avoid reproduction until it’s affordable in terms of your resources. Only when you have sufficient fat are you ready to quit worrying about your own growth and development (you’re already there, according to your hypothalamus) and to shift your focus over to the next generation. There are lots of social concerns about such young girls being reproductive, but evolution doesn’t care – it’s primed to make sure you can have as many babies as possible, to maximize your fitness.
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