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Applejuiceinthehall t1_ivbi7ca wrote

Reply to comment by Frequent-Seaweed4 in TIL that most non-human primate infants actively use their hands to help themselves out of the birth canal. Human infants do not, but their grip strength is much higher during the hours immediately after they are born. by afeeney

Actually, humans have the second longest gestation than other great apes adjusted for size.

The skull size ratio for baby humans is 30% of adult size. For chimps, it's 40% of adult size. So, for humans, that would be about the size at 3 months. There are already women who have hip width that can accommodate that.

Additionally, when studying the gait, wider hips do not make women worse walkers/runners.

So it's probably not that babies came out to accommodate women, but that started being born early for another reason and women's hips width is that size because of baby

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Frequent-Seaweed4 t1_ivbpm2i wrote

We suspect babies started being born earlier because while some women can accomodate a child with chimp-birth requirement, many can't, and this is a population genetics question, not a mendelian genetics question.

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OddEpisode t1_ivbyj2s wrote

I don’t get it

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mrs_shrew t1_ivc9q6j wrote

Women who gave birth to chimp babies more often didn't like it so they stopped/died in childbirth. The ones that were ok with chimps were also ok with normal babies so the survived

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DildoDouchBaggins t1_ivchw5c wrote

I heard the female body has ways to tell if it's a legitimate chimp...

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mrs_shrew t1_ivdv44g wrote

If it's a chimp they can sort of shut it down so it can't continue.

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grumble11 t1_ivc7ctn wrote

Yeah, but if there was a huge advantage like skipping three months of potato-like infancy, women would shift rapidly genetically. That isn’t a barrier if it already exists in the population

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Applejuiceinthehall t1_ivc8ydl wrote

That was the idea, but it doesn't pan out when you look at the evidence. Some women can already accommodate that size skull. So if babies were born with a 3 month olds skull, then the selective pressure would be for wider hips.

Because of women with wider hips, we know that their walking/running isn't impeded with wider hips.

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Frequent-Seaweed4 t1_ivcb6wr wrote

Okay but you keep saying "some" women, when we're talking about the "average" woman.

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Applejuiceinthehall t1_ivceqf5 wrote

But it's only the average because human babies don't have skulls that are 40% of adult skull (which chimps have). If humans were born with that big of skull then women with wider hips would have been selected for and women with narrow hips would have been filtered out

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herbw t1_ivcftpy wrote

Human reproduction is complex system. The pelves of PG woman will expand due to a substance which causes the cartilage of the pelvic bones to relax, so the birth canal widens. to allow easier deliveries. When a pelvis of a woman who has given birth to a child/children is found we can see that on post mortem. How we know it.

Gestating babies, and delivering them is very complex system & has many, many interesting events going on, too.

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Miss-Margaret-3000 t1_ivdfh5y wrote

I saw something interesting from Be Smart recently saying it’s likely a combination of the size parameters and where a human’s metabolic rate maxes out. A woman’s running at approximately just over 2x her normal metabolic rate from crafting a baby once their at 40 weeks which is the majority of peoples maximum sustainable rate. It’s still emerging research, but I thought it made a lot of sense.

edit: Remembered it was a different show

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