How Human Evolution is Shaped… by the C-section?
The C-section has become such a common surgery that it is not always even thought of as such. Instead- women around the world use the procedure as just another way to bring happy, healthy babies into the world. While the indications for when to use this method of delivery are complex, surgeons has garnered recent attention for the disproportionate use of the technique in recent years, especially in the United States and the U.K. Some critics explain these rates as providing a financial benefit to the doctors and surgeons performing the operation, or even laziness on the part of doctors wishing to schedule their hours more predictably. In this article for the Huffington post, Catherine Pearson instead explains some unexpected evolutionary consequences of increased numbers of c-sections that may account for the expanded use of the procedure.
The size of human babies at birth is thought to be a careful balancing act. Larger fetuses are more often healthier, stronger, and more ready to face the world outside of the womb. The fetus is limited however, by the size of the mother’s pelvis (which is constrained by the skeletal restrictions for walking upright). A fetus that is too big would historically risk death both for itself and for its mother. If babies that are genetically predisposed to be born too small die from weakness or sickness, and babies that are predisposed to be too large die in childbirth, the children that survive to pass their genes on to future generations express genes from this middle-ground sweet spot.
Person explains a groundbreaking study by Philipp Mitteröcker, which mathematically models birth sizes over the last few decades, and predicts birth sizes that we are likely to see in the coming years. If his calculations are correct, our medical advancements have progressed far enough to change the course of human evolution. Doctors are now capable of safely delivering fetuses that would have risked death during birth. Removing this upper limit, he hypothesizes, will allow babies to grow up and have children of their own: children that will also carry big-baby genes. Over evolutionary time this could result in bigger babies, and more C-sections to safely deliver them.
While this idea is striking, it is also likely not quite this simple. Medical intervention is now capable of helping underweight or premature babies survive as well, which could disrupt or slow this process. Human evolution is also harder to estimate given the incredible amount of control we have as a species over how we pass our genes along. We are able to treat a wide variety of diseases, and new techniques now even allow babies to be born free of their parent’s genetic conditions. All of these interventions make our evolutionary path much harder to model.
Despite all of this, Mitteröcker’s hypothesis is both intriguing and surprisingly reasonable. Increasing birth rates strongly suggest increased use of the surgery. With any selective bias towards larger birth size, it is not far fetched to attribute this increase to the use of the procedure. More C-sections will prompt the need for more research, but it also marks another fascinating chapter in the genetic engineering that our species is capable of. It is incredible to only now start to understand the long-term impact of the C-section, hundreds of years after it’s invention.
This popular press article summary was written for a Vassar College 2017 Spring course called Sex, Gender, and the History of Medicine. It was part of a unit on Anatomy and Dissection.
