Humans are weird in a lot of ways. With regard to evolution, our species is weird because we’ve evolved so that a fetus’s head just barely fits through mother’s pelvis. This is different than most other primates, which generally have more space to fit the fetus coming out.
The reason for this, say scientists, is the dueling benefits of having both big heads and small pelvises. Big heads are good because they can fit bigger brains, and small pelvises are good for standing, walking and running. So we have evolved to have the biggest heads we can possibly have coming out of the smallest pelvises that will typically allow such a head to pass through. However, approximately 3% of the time, the fetus doesn’t fit. That is, of course, a life threatening complication, and apparently an evolutionary tradeoff.
Enter cesarean sections. Such a procedure has been around for hundreds of years, and more recently has become commonplace, so much so that C-sections now account for 30% of all births, according to the CDC.
Now, the risk of fetal and/or maternal death from the baby’s head not fitting through the pelvis is much less. Because of this, one scientist theorizes that babies will eventually grow bigger and bigger heads because they can, while pelvises can grow smaller. The reason is that, because such traits are desirous, such genes will be able to pass much more frequently, because those bigger headed babies won’t die during childbirth.
There is some evidence that our heads are already bigger than those of people living 150 years ago, and we know that birth weight is increasing as well.
Only time will tell if this scientist’s prediction will come to pass. In the interim, it will be necessary for physicians and nurses managing laboring women to continue to entertain the possibility that baby isn’t fitting, and perform C-sections not only for the benefit of that baby and that mother, but apparently for the benefit of a new version of the human race!
You can read an article that discusses this subject here:
[Has the rise in C-sections affected human evolution? This scientist predicts yes.](http://www.vox.com/science-and-health/2016/12/7/13855350/c-section-evolution)
