We have a very primitive but wise group of Asians living amongst us around here called Hmong. This is a Chinese minority group that has moved down into Laos in the last 300 years. They did not even have a written language until the 1950’s and they have always lived quite a primitive life in the jungles.
Nevertheless, they are quite wise. I read an ethnography on them one time. It said that the Hmong believe that women who get pregnant before 19-20 are more likely to have problems in childbirth. The people who figured this out had no knowledge of modern medicine. But we now know that females continue to develop until age ~18-19. Pregnancies before this age are more problematic because the female’s hips are not wide enough to carry a baby yet. The final widening of the hips sufficient to carry a baby does not occur until age ~19.
You will notice this if you see 16-18 year old girls with killer curves and skinny bodies. They look incredibly hot but their bodies are not natural. It’s not normal to be skinny and curvy. You want curves, you got a bigger woman. You want thin, you get a stick. These girls look this way because the body in a formal sense is fully developed by age 16 in the sense of sex drive, full breast and pubic hair development, menarche and the full curvy body shape with narrow stomach, wider hips and a projecting butt is present by age 16.
Except for one thing. The hips have not yet widened to full adult proportions. So the 16-18 year old girl look is not natural or normal. It is a phase of incomplete development and makes little sense biologically. Since it is not biologically correct, there are increased pregnancy issues at this age range.
When I learned that the Hmong have a traditional belief that females should not get pregnant until 19-20, I was stunned. These humans had learned this via trial and error over the centuries. They didn’t need modern medicine to tell them the facts. They figured them out on their own.
Similarly, the Hmong have a traditional belief that one cannot learn a new language after age 40. This has been a problem in my area because non-English speaking Hmong in this age group simply refuse to enroll in English classes and so never learn to speak English much at all. The men often pick up a bit of English anyway because they are often working, but the women tend to stay at home, so older Hmong women are often Hmong monolinguals.
I told my mother of this Hmong belief and she said, “Aha! See? They figured that out on their own. And they are probably right. By age 40, it will be awfully hard to pick up a new language.” And studies in formal linguistics are showing this to be true.