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
Something you need to keep in mind when it comes to historical medical surveys is that we screen people far more routinely than we once did for a wide variety of medical reasons. Not only that, but a lot of medical conditions/phenomena are not nearly as socially stigmatized as they once were. Thus, we’re much better at finding these phenomena in people. It’s possible that people were always beginning puberty at around 10-12, it’s just that we’re better at noticing it nowadays due to more routine medical screenings.
here you go:
* https://www.google.com/search?q=obesity+in+america
* https://www.google.com/search?q=obesity+and+puberty
* https://www.google.com/search?q=fasting+and+longevity
There’s a few factors but that’s a major one. Also our livestock being pumped full of hormones works it’s way into our foods and some highly processed foods have unexpected impacts on health. Also your caloric intake has an impact on how fast you age. People and animals that generally eat less age slower and live longer. But if you’re looking for one single reason I’d go with “Change in diet”
Proper nutrition and less childhood illness. We didn’t evolve to thrive in perfect conditions but in the actual, realistic ones that were encountered. It’s the same reason people are taller, fatter, and live longer – none of which are necessarily ideal for reproduction.
We’re starting to think that weight is the significant factor in puberty, alongside nutrition and general good health. It is observed time and again that when people are undernourished and underweight they will have a later onset of puberty, and significant weight loss/inability to gain weight as you grow can make puberty become a more stop-start process. Other factors mentioned such as better understanding of human health, routine screening, what puberty is and entails, and even the social side (“teenagers” are a relatively new phenomena from a societal perspective!), also play a role.
Source of that study? If that was true, it would mean that 16 year olds couldn’t get pregnant in the 1800s which without looking into it sounds 100% wrong.
eta: on reflection, that current age of 10.8 ALSO sounds wrong so I question both of those premises.
Puberty normally kicks off at about ~~50kg~~; more childhood obesity and better nutrition = earlier puberty!
Edit: the theory has been updated to refer to BMI and body fat % rather than purely weight.
The number one answer is nutrition. The two major factors in onset of puberty are genetics and body weight. Prior to the post war era, it wasn’t a guarantee that the average person was getting enough to eat.
This is also a bit more speculative, but it’s very possible that women and girls in the post Kotex era are more likely to be honest about these topics. These are self-reported statistics, which will always have room for error. Even today you’ll get allegedly progressive people clutching their pearls and reaching for the smelling salts at the idea of middle school aged girls experiencing puberty, indicating that it is somehow deviant or oversexualized, like something is wrong with 10 and 11 year old girls for experiencing puberty. They’ll blame abuse, media, or “hormones in the food” with zero evidence. And that’s in a society and era that generally accepts that periods exist and puberty happens when it happens. In a bygone era, something seen as “adult” and “secret” may not have been something girls and their mothers discussed openly. It’s entirely possible that some percentage of girls were starting puberty at 12 but saying 16 because that’s a more “appropriate” age.
The research suggests that menarche (first period) is tied to body fat percentage. As Americans have been getting fatter, puberty comes earlier. The effect is less pronounced in other countries that are less fat, like Japan.
It was explained to me in a human development course that precocious puberty is more common now, because body fat percentages in children are getting higher, at younger ages. Fat cells are estrogenic and release hormones which trigger the pituitary to begin puberty.
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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