Why do most women get their first period around age 12 when their bodies are usually not well developed enough to safely carry a baby to term?
In: 12558
Quite simply because this problem wasn’t enough of an issue to prevent women from procreating, so there wasn’t enough pressure to evolve away from it
I don’t know if this is really the answer but I would like to add this:
My gyno once explained to me that during their periods, the girls’ bodies make some certain hormones that help develop their bones structure and shape. So I guess that part of why we get it so much earlier than we actually are able to birth is because it helps us get ready for birth.
Why humans are the only primates that get periods like this, I don’t know, however. Neither when along the evolutionary line we started, although I’d be very interested if someone knows.
EDIT: I stand myself corrected, we are not the only primates who menstruate, apparently some others do, too. Please read the comments below for more clarification on these questions (:
Onset of puberty in young girls is affected by, among other things, body fat % (a function of dietary fat intake and total calories consumed). In early hominids, young females likely didn’t acquire enough calories, and calories from fat, to start puberty as early as they do in developed nations today.
Edit: fking auto-incorrect
I got mine at 13. I’ve heard modern diets- both from the perspective that we have better nutrition that allows this to happen, and negative impacts that affect hormones have bumped this age lower in recent history. The average kid is also now swimming in a sea of endocrine-disrupting exposures in their daily life from plastics and synthetic fragrances and other compounds.
All that said, there are breast changes that happen with each menstrual cycle (growth of ducts and the actual tissues that make milk), that prepare the woman to breastfeed said baby some day in the future also. I would guess that the short answer is evolutionary compromise. Perhaps from an evolutionary perspective, it’s better to begin ovulating and prepare the body, even if it runs the risk for the occasional bad outcome.
Others have covered some facets of this such as puberty/menarche starting earlier now than in the past on average for various reasons, but also worth noting that the first few periods a girl has are usually anovulatory. Meaning no egg is actually released. Ovulation (egg release) requires certain hormones to reach a threshold in order to happen and while those hormones are fluctuating enough to cause bleeding (progesterone withdrawal) when a girl gets her first period, they are not high enough (LH/FSH) to release an egg. This could be the case for just one or two periods in some girls, or periods could be entirely anovulatory for up to a few years in others.
A girls first period happens relatively early in puberty, it isn’t the conclusion of it. The age of onset of puberty for each individual girl is determined by a combination of genetics and body weight. We live in a time of plenty, so prior to the post-WW2 era, girls were hitting puberty later (12 is an average now, it’s not a rule. Similarly, 14, 15, 16 would have been average at various times in the past, but not a rule).
I think, simply, people *in general* have always known that 12 was too young, or “just got their period” was the start of maturity, not the conclusion, so wait a few years. Everyone? No. But enough that dying due to premature pregnancy was merely a risk, not something that decimated the species. Modern humans have generally been smart enough not to impregnate 12 year olds as a general rule. So there’s never been any need for our development to change drastically.
There are cases of modern athletes and women in the 19th century not having a first period until late teens. Meanwhile there’s also cases of menarch under the age of 10. The actual difference has to do with estrogen levels and body fat levels. Essentially body fat has a hormonal effect of estrogen, and enough of it or lack of it can contribute to having periods or not. If you want to think in terms of evolution, then during times of extreme famine getting pregnant may be a hindrance to survival, whereas times of plenty would be a more opportune time to get pregnant.
This may be out dated information, though. It could be I haven’t read the studies debunking the articles I had read from over a decade ago.
Didn’t know that was the average. I was 15, my sister 13. I am the older sister, developed much later and am often mistaken for the younger sister even with my grey hair(I’m almost white at 36 which is common in our family). I was very very premature at birth so that may play a role in it.
A girl’s period happens because she starts puberty, which is when the body starts ramping up hormone production that leads to adult-type development. It happens in both girls and boys. The gonads/sex organs of both sexes mature and release hormones that cause the rest of the development that we know throughout the body (breast development, growing taller, larger penis and testicles, underarm and pubic hair etc.)
Since the same hormones that cause puberty cause periods, it would be impossible for a woman to develop without having a period first. It’s a kind of a “Chicken or Egg” scenario. Their bodies would never develop enough to “safely carry a baby to term” as you say without having periods, but periods make it so they can get pregnant young.
Interesting article. Girls are getting their periods on average 2 years earlier than they were just a century ago
https://www.scientificamerican.com/article/why-are-girls-getting-their-periods-so-young/
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