Monday, May 10, 2010

Wenda Trevathan's "Ancient Bodies, Modern Lives"

Wenda Trevathan is the Regents Professor of Anthropology at New Mexico State University. A biological anthropologist whose research focuses on the evolutionary and biocultural factors underlying human reproduction, her publications include Evolutionary Medicine and Health: New Perspectives.

She applied the “Page 99 Test” to her new book, Ancient Bodies, Modern Lives: How Evolution Has Shaped Women’s Health, and reported the following:
Page 99 of my book Ancient Bodies, Modern Lives: How Evolution Has Shaped Women’s Health is given over to a discussion of pelvic organ prolapse (POP), not the most attractive of the health problems I talk about in the book. My first reaction was to dismiss the whole idea and argue that it isn’t representative of the book, but, on reflection, it actually does a pretty good job of exemplifying the arguments I make. The evolutionary process has involved a number of tradeoffs over the course of human history; very few of the fundamental characteristics that make us human has required more compromises than the evolution of bipedalism, or two-legged walking. In fact, there are a number of medical specialties that owe their existence to the fact that we walk on two legs, including orthopedics, podiatry, physical therapy, chiropractic, osteopathy, sports medicine, and obstetrics/midwifery.

Another fundamental characteristic of humans is our large brains and heads, and just as natural selection was favoring a narrow pelvis for bipedal walking, it was also favoring increased brain size. This helps to explain why birth is so much more challenging for humans than it appears to be for most other mammals. In a four-legged animal, the tough muscles of the abdominal wall contain the internal organs in a sling beneath the spine and their weight is spread out evenly along the horizontal support. With the shift to bipedalism, the organs are now packed in the bowl formed by the pelvic bones and they are squished downward, sometimes spilling forward out of the basin, putting strain on the abdominal wall. Too much strain can result in small openings in the lower abdomen through which the intestines can spill known as hernias. The abdominal muscles provide only a little support from the front, so it’s up to the muscles and ligaments in the lower pelvic basin to do the hard work of holding the organs in and keeping them from falling through the pelvic opening. Unfortunately, sometimes they do fall through, resulting in the medical disorder called pelvic organ prolapse or POP. This is thoroughly discussed on page 99, but if that’s all you read, you’ll miss a lot of the more interesting topics including the health consequences of early puberty, highly frequent menstrual cycling, difficult births, breastfeeding, and menopause.
Read an excerpt from Ancient Bodies, Modern Lives, and learn more about the book at the Oxford University Press website.

--Marshal Zeringue