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Health Center Today, February 11, 2011

Can C-sections Influence Evolution?

By Chris DeFrancesco

Photo of Dr. Joseph Walsh

Dr. Joseph Walsh has a letter to the editor published in the February American Journal of Obstetrics & Gynecology.

A UConn Health Center obstetrician-gynecologist suggests there are human evolutionary implications to the advent of cesarean section as a reasonably safe delivery method and the subsequent rise in the rate of C-section births.

Specifically, Dr. Joseph Walsh believes the rise in C-sections may be both a cause and effect of the trend toward higher birthweight babies.

It’s a concept Walsh introduced less than three years ago and is reinforcing with a letter to the editor of the American Journal of Obstetrics & Gynecology, considered among the most prestigious journals in ob-gyn. It’s published in the February issue. February 12, 2011, marks the 202nd anniversary of the birth of English naturalist Charles Darwin, generally accepted as the father of the theory of evolution.

Walsh suggests a Canadian study linking a rise in induced labor to declines in birthweight and gestational age left out evolution as a potential factor in the trend toward increased birthweights before the study period.

“Prior to the availability of cesarean section, women with a small pelvis, and babies of large birthweight, were at risk of significant morbidity and mortality. With cesarean section, selection against a small pelvis or large birthweight has been all but eliminated,” Walsh writes. “The maternal pelvis can get smaller over time, and fetal birthweight can get greater over time, because there is now nothing to limit these changes.”

In the same letter Walsh refers to his article published in the September 2008 American Biology Teacher, in which he wrote, “The C-section rate will continue to rise, because the ability to perform a safe C-section has liberated human childbirth from natural selection directed against too small a maternal pelvis and too large a fetal head. Babies will get bigger and pelves will get smaller because there is nothing to prevent it.”