I see how other animals stand and walk literally 10 minutes after they’re born but as babies all we do is cry and eat, why aren’t we like other animals?
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Our adult brains are really big, and our pelvesis are not that wide.
We need to be born with really immature brains so our heads can fit through the pelvis.
Humans are trying to build a gigantic biological supercomputer in their heads, and this takes several years to assemble.
We also have very narrow hips to walk upright.
So this created an evolutionary conundrum: the finished brain doesn’t fit through human hips.
So there’s only one solution – human babies are born extremely “undercooked” so that they still fit, and then most continue developing for a long time after birth.
Our huge brains mean we have big, fat heads. And our walking on two legs schtick means we have relatively narrow hips, for better balance.
This is an issue for childbirth. Our big fat heads have to slip through the hip bone of the mother. Some women have pretty wide hips, but that opening is only so big.
The compromise evolution came up with was to essentially have our species give birth when the babies are still “undercooked”. We need them to come out of the womb early, before their skulls reach full size and harden, so they don’t risk a really nasty birth complication.
Because we evolved to favor large brains over other things. Unfortunately, our large brains and skulls are too big for the anatomy of women to give birth to, so we also evolved to give birth before the baby is as physically developed as some other animals. A ton of growth development happens in the first year. In fact, the 1st 3 months after birth is referred to as the 4th trimester because of how much development takes place. It is almost as if they should be born 3 months later, but that would have ended up killing most women, so evolution took the other path.
Animals that evolved to be able to get up and walk so quickly are generally grazing, or herd animals, and evolved that way as a survival mechanism, to be able to move with the herd and keep away from predators. A human can pick up and carry their baby to safety, but cow or horse can’t.
It’s a biological payoff for two things we do that others don’t; walk upright and having larger brains.
Tldr: our species made a compromise by having our babies at a more immature stage and needing more care so we can go on to walk upright and be more intelligent than other species when we grow up. Otherwise most women would die in childbirth when their bodies split out delivering a two year old!
Since we walk upright our pelvises are shaped differently that other mammals, and even different from other primates (similar general appearance but ours are proportionally narrower). Our pelvises are narrower so babies need to be born at an earlier stage of development that other species so that the head doesn’t get stuck.
The other part is that, compared to our body size, we have large heads because we have larger brains that other species. And they will continue to grow relatively rapidly in the first few years of life. If you look at World Health Organisation growth charts the head circumference section only goes up to 2 years of age, as by that point your head isn’t going to get that much. Look at some 2-3 year olds head sizes and think about pushing that through a north canal.
Because of the combination of having bigger brains but proportionally narrower pelvises than other species, evolution compromised and we give birth to offspring at a more immature stage than other mammals.
It can be a difference between predator/prey animals.
Kittens/Puppies/Bear cubs are born quite helpless as well, there’s nothing hunting them. Herbivores had the need to get up and run away from any predator wolf/lion/etc.
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