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Cesareans: Labor-intensive childbirth

by Archives February 8, 2006

EDMONTON (CUP) — Recently, I was considering the unique nature of human pregnancy, and some of the unaddressed consequences of modern methods of childbirth. Because humans walk upright, have disproportionately large brains compared to other mammals and are now, more than ever before, removed from almost all natural selection, it puts us in a unique position.

In the past, there were two relevant selection pressures on a human female. First was the development of the fetus’ enormous brain-a defining human characteristic. Leaving aside the contentious question of why the brains of our ancestors expanded so rapidly in the first place, the development of the fetus’ brain had an enormous effect on the pattern of human pregnancy and birth.

There was a balance between the development of the fetus in the security of the womb and the need to give birth before it got too large. It’s for this reason that human babies in particular, and large-brained primates in general, are born so underdeveloped.

The infant couldn’t be kept for too long in the womb, however, because there was also a delicate balance between a broad birth canal, capable of accepting a large-headed baby, and a pelvic girdle structured for efficient bipedal movement-the second pressure. Too narrow a birth canal could result in the death of the mother and child during birth, but a canal too broad, with hips wide enough to accommodate it, would interfere with bipedal movement, again threatening the survival of both mother and child. So the need to walk upright combined with the need for the large human brain determined, within a very narrow limit, the structure of the female pelvis and birth canal.

But “cesarean sections changed all that,” said Frans de Waal, a distinguished primatologist. The shape of the pelvis is no longer constrained by natural selection.

Approximately 28 per cent of all North American births are now done by cesarean section, a five-fold increase since 1970. Most of these C-sections are done because they’re more convenient than vaginal births, or because the pregnant mother fears the pain of childbirth, to protect the doctors and the hospital from lawsuits, or due to unforeseen medical complications, such as a breach baby or an outbreak of genital herpes. But not all of them. An increasing number of cesareans are being done because the birth canal is too narrow, endangering the safety of the mother.

De Waal continued, “More and more women with narrow birth canals will survive, passing on a trait that a few generations ago was a death warrant. The inevitable result will be a growing number of C-sections until natural birth becomes the exception.” The assumption being, of course, that our current level of medical funding and expertise can be sustained.

But this isn’t necessarily the case. Cesarean sections require obstetricians, anesthesiologists, nurses, custom tools, drugs and antibiotics. Yet all of these things are dependent on a stable, robust economy. If our economy is disrupted, either through failure to find an alternative to oil or through rapid environmental change-the two most pressing possibilities-cesarean sections will no longer be possible. This means that those women who have inherited a narrow birth canal, if they become pregnant, will die during childbirth.

This is a particularly morbid example of something that’s happening across many human traits. Because in our modern civilization we’re almost entirely removed from the influence of our environment-and natural selection-many deleterious traits are free to spread through the population. Our allele frequencies are shifting and, because there’s no pressure to direct them, the shifts are essentially random, spreading out from an adaptive mean.

This is an issue that must be addressed-by our scientists, by our politicians, by our doctors, and by each of us as individuals. We can’t afford to pretend that this isn’t a real phenomenon, with real consequences, or that the potential for abuse absolves us of the responsibility to seek solutions.

We have an obligation to the generations that come after us to leave a habitable world, with ecosystems capable of supporting them. We also have an obligation-every bit as real-to leave behind adaptive genes.

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