So, I have a couple degrees in anthro...and I also just love replying to interesting threads on MDC.
First of all, natural selection operates on the level on the individual and on his/her ability to reproduce successfully. So, to use the dentist's example, a woman might, through some random mutation, end up having teeth and a jaw just a bit more suited for her diet. Those teeth would give her a slight advantage so that she would survive to her childbearing years and have a bunch of children. Some of those children will have her nifty dental features and some would not. The children who did would be at a slight advantage and, over millions and millions of years, everyone in the population might come to possess those features if they were a true advantage to reproduction.
Not just an advantage to eating but to reproducing...
On the other hand, she could end up with a variation that isn't naturally selected for, like, slightly pointier canines. Let's say, she lives in a vegetarian society so there's no natural selection pressure to rip into meat. They don't hurt but they don't help. But, for some reason, males really dig those pointy chompers so they are sexually selected for. (If everyone thought that having pointy canines made you unworthy to be a mother, they would be selected against even if they were neutral in terms of natural selection.)
So, I disagree with the dentist's POV. The jaw has
become progressively smaller over time, leaving less room for wisdom teeth. And, yes, that is in response to our changing diet as well as to other changes in the shape of our skulls---big old neocortex, voice box shaped for speech, sexual selection for chins, who knows? Let's say, for the sake of argument, that natural selection has selected for
those who don't produce wisdom teeth since that gives them a slight advantage somehow. They're slightly heartier because they don't have to invest in those totally unnecessary teeth, they don't have a risk of impacted/infected teeth, they mate more because they have better breath, etc.
So one view might be that surgical removal of wisdom teeth is actually interfering with the process of natural selection, since it's allowing people with the genetics to produce wisdom teeth to masquerade as non-wisdom toothed individuals with all of those same advantages. In the same way, let's say women favored men with smaller foreskins---not saying this is true, ladies---but, if it were, and if sexual selection had its way, the foreskin would get smaller and smaller over time. Or, heck, let's say women favored foreskins that were a little darker or shaped in a cetain way or whatever. It doesn't matter. What matters is that surgically removing the foreskin disguises the natural variations in foreskin size (and shape and color) so that sexual selection can no longer operate on that feature.
What that means is that kids will continue to be born with or without wisdom teeth, but, in the US, among those with dental care, that factor will not be worked on by natural selection.
Okay, so now to surgical birth. As everyone in this forum already knows, human babies are born very very prematurely compared to other primate species. The reason is that human babies have big brains and women need to be able to walk. The pelvis is the limiting factor. It's as big as it's gonna get down there. So, over millions of years, natural selection has operated on the baby---favoring those cranial plates that can mold during vaginal birth, favoring babies that were born earlier so more brain development could happen during the "fourth trimester," etc.
Back in the day, when there was a true "mismatch" between pelvic size and baby's skull, women would die and so would their babies. If the baby was born too early, the infant wouldn't survive. So there was INTENSE pressure for the pelvis and the baby's head to be in perfect balance, size-wise, and for the baby to be born just mature enough to be able to make it in the outside world. Women today are the result of this intense pressure since, if our ancestors weren't able to birth vaginally, and babies weren't born at the right time, we wouldn't be here. Even c/s babies didn't typically survive long unless there was a wet nurse available...and the moms never survived.
So, the increase in surgical births, is removing this intense pressure on pelvic size and baby head size since women with smaller pelvises and babies with bigger heads can survive. Again, these are rare circumstances---probably less than 5%---since we are the result of millions and millions of years of pressure to keep head and pelvis in sync. But, since surgical birth has only been truly possible for a few decades, I don't think it will have any effect on evolution or the ability of children born by c/s to give birth vaginally. And, again, those kids would have to be selected for
so that small pelvises or big heads would become an advantage rather than a neutral feature.
BTW: I think it's a good thing that we have technological advances that allow infants and mother who would have died to survive. I'm glad that we can supplement with formula for the 5% of moms with low supply. I'm glad that we can perform c/s for the 10% of women with medical conditions that make vaginal birth an impossibility. But I think when you have c/s rates---especially elective c/s---and formula feeding rates as high as they are in the US, then something is tremendously out of balance.
Can you tell that my DS is napping so I had time to type this?
wombatclay: I enjoyed reading your post, and I'm glad that there are other long-winded anthro folks on MDC!