Well, we have these ridiculously large heads, see, even as babies. And we insist on this walking upright thing, which means our pelvises aren’t all they could be, and the hole the head has to pass through is at right angles to the birth canal. (Yeah, “intelligent design,” my ass!) So first we tried* having our babies sooner, before they’re really fully cooked. Works for the kangaroos, right? So instead of a nice year long gestation, we have 'em around 40 weeks. Sure, the babies are completely helpless at that point, but if we pair bond to our mates, someone can go find the food while the other person holds the baby for 6 months. Hmm…maybe pouches would be a good idea…
That still wasn’t quite enough, so next we tried collapsing the skull of the infant in the birth canal - the bones slide one over the other to make the huge thing a little smaller. That seems to do the trick, most of the time, but it still takes time to encourage bones to move like that. And there’s still that weird right angle to get around. Babies still get stuck on pelvic bones distressingly often. Sometimes they can be moved by changing the position Mom’s laboring in, but sometimes they won’t budge, and you need progressively greater interventions to get them out before Mom’s too exhausted to push anymore.
And then there’s the social and mental handicaps. We’ve decided to hide away our real women giving birth and replace that experience with overly dramatic actors shrieking on television and going from first (excruciating) contraction to delivering a 5 month old in about 14 minutes flat. For many women, the first real birth they ever witness is the one where the child is coming out of them. So we’re terrified, which never does good things for relaxation of large muscle groups, and we’re ignorant, which is rarely useful when it comes to doing new things.
And we *think *all the time, which means “instinct” which, as far as we know, guides all other animals through this process, doesn’t work so well with humans. So because of the ignorance thing and the thinking thing, we want guidance and assistance.
We don’t deliver like other animals because we’re not like other animals, in this particular instance. Some of that is through biology (some breeds of bulldog require intervention at birth for some of the same reasons we do) and some through social conditioning and fear.
Do I think (most) women would be (mostly) better off if we lessened the default level of intervention? Absolutely, no question. But I wouldn’t want to give birth totally alone, either.
*speaking metaphorically, of course. And possibly out of order.