I’ve wondered this for a while, but my other thread finally made me ask the question: Why is pregnancy so dangerous?
Millions of women over the millenia have dies in childbirth, which seems a bit odd to me. I know that horses and cows can have difficult childbirths, but every nature show that I’ve seen shows the baby gizelle/waterbuffalo/giraffe etc fly out with barely a grunt from the mother. Now I know that its an incredibly traumatic event, and so would probably lead to a good few deaths, but other animals don’t seem to have the same trouble as humans.
Surely we should have evolved towards a decent way of giving birth? Why are there still women with narrow hips even those make it even harder to give birth? Yes, they’re move attractive, but shouldn’t they have been bred out long ago?
I know that modern babies are bigger, but that doesn’t account for past trends.
One theory is that because we’re capable of assisting each other in giving birth, that’s removed some of the selection pressure on women to have wider hips.
Basically it’s because the human brain, and hence the human head, has vastly increased in size over the course of the last million years or so, and the hips have not evolved fast enough to keep up. It’s also why human newborn babies are so relatively helpless - in order to get them out of the womb at all, they have to go at a far earlier stage in their development than most other mammals.
As fast as we evolve better childbirth, we evolve bigger braincases in newborns, and the latter is effective at promoting survival and allowing genes to be passed on. What’s bad for some mothers isn’t necessarily bad *enough *for the species as a whole, so it doesn’t get bred out.
The price of walking upright and having a large brain is difficult childbirth. Apes give birth far more easily because their pelvises are made differently; our pelvises have to walk upright and take a lot more stress, so the baby has a more difficult passage because of that. At the same time, the baby has a huge head. Therefore human babies are born half-cooked compared to other mammals; it’s a compromise, because if pregnancy lasted longer, the baby wouldn’t be able to be born at all. So childbirth is this complicated balance of baby’s maturity, mom’s pelvis, and the human large brain.
As long as it works well enough to keep the species going, it’s good enough for Mother Nature.
Because a woman’s hips are “dual use.” Narrow hips are better for walking; wide for childbirth. So, you have selection pressures working both ways, with the result being hips that are less efficient for walking than a man’s, but narrow enough to make childbirth difficult but usually survivable.
And as for why we haven’t “evolved towards a decent way of giving birth”; it’s because evolution has no foresight, and the right set of mutations hasn’t occurred. For example, adding a set of swivel joints that allow the hips to open much wider in childbirth but remain narrow most of the time would be better *; but the genes for such an arrangement don’t exist. And unless they or something similar happens to appear, evolution can’t select for them. Serendipity is a powerful force in evolution, since selection pressure can only work on qualites that already exist or just happen to appear.
You have to remember evolution doesn’t do what’s best, it does what works.
Look at it this way millions of people have choked to death on food. But billions more don’t. Having the airway and the food tube cross isn’t the best plan but for the most part it works. Once something is done evolution doesn’t back up and change the plan.
As long as more women DON’T die in childbirth than do die, that is all it takes for evolution to stay the course.
Of course now humans can intervene and perhaps more women with narrow hips, that would’ve died now can live (via medical intervention) and those genes pass on.
You can’t ask “why hasn’t this happened?” when you’re talking about evolution, only “why has this happened?” We can come up with all sorts of improvements, but the only reason they haven’t appeared is that they haven’t appeared.
Because this is what works best for those animals, so evolution has selected for that.
Remember that these are all prey animals, that need to be able to run fast to avoid predators. The mare has to give birth quickly, and the foal has to be able to travel with the herd soon. Unlike humans, where the infant is utterly helpless for the first couple of years, and can’t really be out on it’s own until age 15-20.
Having raised horses, I know that a foal is expected to stand & nurse within the first hour of it’s birth, and to be able to run and keep up with the herd by the time it is 24 hours old. (I don’t know about gazelles, waterbuffalos, or giraffes, but I expect they are similar.) Mares that take too long to give birth, or need assistance, or produce foals that develop too slowly have been eliminated from the species – they were eaten by predators.
The occasional difficult births for horses & cows are mainly a result of humans overriding evolution and producing specialized breeds for our purposes, without concern for the evolutionary need to run with the herd to avoid predators – that isn’t important any more when the animals are domesticated and raised & cared for by humans.
It’s a shame we weren’t descended from marsupials – babies would be born at a premature stage, then raised to full development in the mother’s pouch. Not only would this bypass the whole brain vs. pelvis bottleneck, it would add a brand new dimension to pornography.
