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
can anyone with Ob-gyn experience explain what is a “safe” age for girls to be able to carry a baby to full term? I was just thinking about this in another thread revolving around House of the Dragons, where it was suggested that the widower King betroth a 12yo girl to produce a royal male heir.
The WHO has some [information ](https://www.who.int/news-room/fact-sheets/detail/adolescent-pregnancy) regarding adolescent pregnancy:
> Approximately 12 million girls aged 15–19 years and at least 777,000 girls under 15 years give birth each year in developing regions.
I found this [reference ](https://obgyn.onlinelibrary.wiley.com/doi/10.1111/1471-0528.12630) particularly interesting, as it gives a breakdown of outcomes for mothers in different age groups.
I think the issue here is an issue many people always have. They think that because we have evolved this way that there’s a reason for it. This belief that evolution is well calculated. It’s truly not, some traits live on simply because they haven’t been damaging enough to kill off a species. Like those goats who’s horns grow into their skulls and kill them. There’s not evolutionary use for that but it happens. This could just be an example of that because, while it sucks that mothers die I’m childbirth, that hasn’t harmed our species a whole lot. Although it could be bred out eventually, that’s probably why we like women with wide hips so much.
You could also wonder why humans are among the few species whose newborns cannot survive by themselves during months, if not years. I believe it’s just because there isn’t evolution pressure against it.
Real ELI5: Pokemon aren’t ready to do battle as soon as you catch them. They need to be trained. And then if you train them right, they evolve into their final form.
The same is true for human fertility. It takes time for all the bits to grow or change into their final form. Some bits, like the lining of the womb can develop pretty quickly once the right hormones are working. Other bits, like the size of the bones a baby has to pass through during birth grow and evolve much slower.
A girl getting her first period means that the mix of hormones in her body are now much closer to the adult mix than the child mix she used to have.
A completely non-human example is here:
Young mammals of *many* species such as goats, dogs, and more go into a heat cycle before they are capable of safely bearing young. They can absolutely get pregnant, and die giving birth, or give birth to young that can’t survive.
In the wild, if you survive and the baby survives, you’ve still reproduced, which gets you a score in the evolution department. The evolution department doesn’t give a damn about side effects as long as the line continues.
The way many communal species handle this issue is that they frequently have older females or pairs stop the younger animal from breeding. This is done through violent or social means, and it can involve driving away potential mates, reducing food, fighting, or calling over their younger members so their breeding calls can’t be heard. Dominant pairs will stop animals that are too young to safely breed from breeding, if they can.
In other words, smart social species ensure their young members are old enough to safely breed if they start cycling earlier.
Evolution doesn’t need to make ethical or rational sense, and usually doesn’t. You’re not looking at the steady, unstoppable march of progress. You’re looking at “eh, good enough” times a few hundred million. It overcorrects, it undercorrects, it fails, *a lot*. Species go extinct, and your existence right now owes less to your indomitable genetic superiority and more to the fact that, with an incomprehensibly large number of us, there is plenty of room for a whole lot of people, you included, to get lucky that “good enough for another generation” worked in your favor.
All “evolution” strictly requires is that *one* of a mother-child pair survive birthing. A surviving child is another generation. A surviving mother can typically try again. Our individual histories could be littered with a lot of young mothers dead way before their time, and our long-term species legacy certainly is, but it still gets us here, not because we are “strong” or “fit” but because our ancestors happened to just barely survive whatever happened to them.
So all that being said, the age at which women *can* become pregnant and, on the whole, either she *or* the child survives the experience, is a whole lot lower than the age at which they can both share the experience “safely.”
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