See into these C-Sections

Recently I babysat for a couple who wanted a night out. As they told me about their precious little parasite, one thing that caught my ear was that she was a delivered through a Caesarean Section rather than natural birth. Through some medically related classes that I've taken at Rice University I've been hearing how there has been an increase in the amount of C-sections done. Although many attribute this phenomena to the availability and convenience of the procedure, I began wondering if evolution could actually be a major factor in this increase of C-sections.


Of course, research needed to be done and I scoured through Google Scholar and the Fondren Library for articles that could potentially let us see more clearly in this C-Section phenomena. Many articles concur that there has been rising rates in caesarean sections of approximately 10-15% in the World Health Organization [1]. However, delving specifically into the idea that evolution explaining an increase of c-sections, apparently one reason linked to evolution is that the human body is rather like a hunter-gather's body living in the 21st century. While society has changed so that women have become fatter (sigh) and more likely to give birth at an older age. However, evolution has not occurred through natural selection on women's' bodies to adapt to those social changes.  So ultimately, the article concluded, "cultural evolution has outstripped biological evolution."


I quickly dove back into the mess of articles to see if anything else corroborated these everyday evolution events happening in our very midst (well, not mine or yours, but "ours" as in humanity's). And I promptly stumbled upon another article at that discussed the conflict between the maternal pelvis and fetal head size in terms of selection pressure [2]. In this article, it was concluded that human birth has always been constrained by the size of the birth canal  and pelvis (oh lovely images), and that those babies with larger heads than normal before C-sections would die from cephalopelvic disproportion. Thus, pelvis size has always been a negative selection on the size of babies' heads.


The article goes on to speculate about the increase of IQ that might be seen in the future due to the introduction of C-section, and consequently the survival of big-headed babies.  However, I find myself a little skeptical about that. But who knows, maybe the baby I watched over recently is going to be a genius - after all, she did come from a C-section birth, the newest removal of a negative selection force.

 -Karen Lin


[1] Liston, W. A. (2003). Rising caesarean section rates: Can evolution and ecology explain some of the difficulties of modern childbirth? Royal Society of Medicine (Great Britain).Journal of the Royal Society of Medicine, 96(11), 559-61. http://search.proquest.com/docview/235006270?accountid=7064
[2] Walsh, J. A., M.D. (2008). Evolution & the cesarean section rate. The American Biology Teacher, 70(7), 401-404. http://search.proquest.com/docview/219029276?accountid=7064