I hear of women in my community and across the world either having stillbirths or dying during the process of birth all the time. Why?
How can a dog or a cow give birth in the dirt and turn out fine, but if humans did the same, the mom/infant have a higher chance of dying? How can baby mice, who are similar to human babies (naked, gross, blind), survive the “newborn phase”?
And why are babies so big but useless? I understand that babies have evolved to have a soft skull to accommodate their big brain, but why don’t they have the strength to keep their head up?
In: Biology
Humans have a huge brain, which requires a big head, and getting that head out of the mother is very hard. Humans walk upright, rather than on all four legs, and that leads to less spacious pelvic geometry.
For a baby to mature, and build strong muscles, it needs to use its brain to control those muscles. To program the brain, you need to get the baby out into the environment where moving your head is good for something.
Evolution gets you what’s best for survival, and it turns out that upright walking and a big programmable brain is more useful that a small brain with more instinctual behaviors. Birth only needs to be “good enough” that many infants survive.
Almost all the questions you had around human vs other animal birth (regarding difficulty, or how the other animal can just walk instantly) is based on our brain size.
Humans have big heads, huge heads. The heads are so big that we have trouble fitting through the birth canal. The solution is to give birth to the babies earlier than they’re ready and then care for them externally. In fact a few other animals have a similar strategy like marsupials that birth their young and then carry them in a pouch that is sort of like a womb-lite.
So in a way of thinking all humans are born premature, which is why we’re so helpless as babies. Of course we’re born as little premature as possible for our survival, which is why the head is still pretty big and hard to pass.
Result? Premature babies are worse at just about everything, like holding our own head up, but that isn’t too much of a drawback because we have the ability to care for our young well.
Bipedalism (walking on two legs) forced the birth canal of hominids (human ancestors) to narrow. A feedback loop between improved cognitive abilities and being better adapted to exploit the environment caused our ancestors’ brains to grow. Between the narrow birth canal and enlarged brain, human babies have to be born less mature than other apes. That’s why they aren’t able to hold themselves up quickly like a baby chimpanzee can. Our social adaptations mean that mature humans can continue “gestating” babies outside the womb. So, it isn’t a perfect system, but it is successful enough (aka highly successful) that despite the issues and limitations it wasn’t ever selected against evolutionarily.
Dogs and cows can give birth in the dirt, but without human monitoring and intervention, they die at higher rates like anything else, they just tend to go to secluded places so you never see dead mom and babies on the side of the road unless a human person put them there. Add to that, scavenger animals exist and come eat the dead bodies, so the secluded dead aren’t there for very long and recognizable.
While it may be dangerous and inefficient, from a evolutionary perspective it works, there’s 8 billion of us.
Humans have comparatively big heads to most other mammals, we also walk upright on our feet
Not much room for that in a uterus, much less the birth canal
Technically, all human babies are born premature. All other animals come out fully functional, able to walk and run. Because of our big heads and big brains, only women that can give birth to premature babies can produce a baby small enough that won’t kill the mother. In a weird way, evolution has selected for humans that are born premature. This reveals what an incredible advantage being a smarter animal is, to the point that bigger, stronger, more physically viable members are discarded by nature for smaller, smarter ones.
Animals die during birth *all the time*. You just don’t see it in the wild and most laypeople aren’t breeding their animals. Breeders see it frequently. Vet intervention is common for certain breeds in order to save mothers and babies. Birth is traumatic and dangerous no matter what you are.
because it works.
this is quite literally the one and only answer to any “why” question about evolution
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