Is it because of the whole big head/bipedalism thing? Other mammals can pop out babies in no time and it seems like that would be way more advantageous for multiple reasons (less stress on mom and baby, not in a vulnerable position for hours in the wild, etc). Why does the norm skew towards a day rather than hours?
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It almost all comes down to our upright posture combined with our high intelligence.
Our high intelligence requires a big brain, but our upright posture requires relatively narrow hips or else it is very difficult to walk.
So the current situation of having very difficult childbirth is essentially an evolutionary compromise between those 2 requirements.
You are right about the big head and bipedalism which both makes child birth much harder for humans then other animals. And this would indeed make it quite hazardous for humans to give birth in the wild. Not only would it attract predators but infections are much more likely as well. And even just the exhaustion from the event might prevent someone from gathering food and water to survive and recover.
So human child birth is only possible in an intelligent species with social structures and planning skills. The rest of the family group is needed to protect the mother and child and provide for them during the process. Some of these intelligence traits likely evolved first which favoured people with larger heads capable of standing better as the survivability of complex births went up which again allowed people to be smarter and work better. Even though there are some branches on the evolutionary tree of humans compared to a lot of other animals the evolution have been very straight forward with people being smarter and smarter for every generation. Other animals have just not gotten into this intelligence niche which humans have evolved into.
It is not quite true that humans are the only animal with such complex births though. Although the other animals with such hard births are bred by humans. Some species of cattle and sheep are completely unable to give birth without human intervention.
Two big reasons.
1. We are bipedal. Our skeletal system has evolved to better support standing on 2 legs, but that makes it worse for childbirth.
2. Our heads are huge. Human children are born earlier in their development cycle compared to other mammals (most mammals can get up and move within minutes of being born, humans take months). This is because any later and our heads wouldn’t fit. As it is, our heads are still huge coming out, and that makes it difficult.
Because we walk upright and have large brains.
Walking upright requires that we have narrower hips, which means narrower birth canals.
Large brains mean we need big heads, which are hard to push through a narrow birth canal.
This is also why human children need so long to develop. Our brains can’t fully develop in the womb like other animals because then our heads would be too big to fit through the birth canal.
One additional thing that people are missing, modern birthing, especially in Western countries, is set up for the birthing DOCTORS comfort not the birthing parent(laying down in stirrups so the doctor can sit and watch the birth happen). When people give birth in a squat position it’s generally a faster and smoother birth.
Evolution doesn’t choose where to change things, it changes random things and the benefits can cause more reproduction among creatures with those traits; natural selection, and survival of the fittest.
In humans, it was intelligence that was evolved, but that costs more time and energy to reproduce. However, it was intelligence that allowed us to live longer in order to further develop humans with even more capability for intelligence.
Of course, this happened over millions of years, but that’s how we got here. In the wild we were weak, but our intelligence paved a way to survival. Not to mention bipedalism, which allowed us to run for miles without even breaking a sweat. Combined with our intelligence, we could run animals off cliffs and we would have spent much less energy for much more reward…
And the cycle continued. Evolution didn’t directly change the way we reproduce because we were living much longer with intelligence and bipedalism, and as a result we kept those traits.
Having a “den” or “pack” that allows newborns to grow more and be protected by the group makes this possible. If we did not nurture babies together and left a mother and baby on their own survival would be rare and we would never have been able to evolve the larger brains.
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With bipedalism the pelvis had to decrease in size
But then with bigger heads a bigger pelvis is needed
So a good enough balance between the two evolved. This is why women have wider pelvises than men, if not for childbirth the ideal width would be that of a male pelvis
Are ancestors would just squat down and deliver the baby, often by themselves. Death for the mother, child, or both during childbirth were common.
Now death during childbirth is rare because of helpers, tech, and medicine.
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