Look for the term "pelvic canal" in the Anatomy Manual or in this manual. Typical obstetrics, and you will probably find a description like this: "Well-built women, who had a good diet during the growing period of their childhood, usually have a large pelvis. "

Such a basin, continues the text, allows" the slightest difficulty during childbirth. "

But such characterizations have long been based on anatomical studies of human subjects. European pedigree In reality, the structure of the pelvic canal, the bone structure through which most of us enter the world, varies enormously from one population to another, according to a new study published in Proceedings of the Royal Society B.

for how obstetricians treat patients of color, say the authors.In the United States, for example, the risk of death related to pregnancy is three Four times higher for black women than for white women.

"What worries me is that doctors are coming out of school thinking about Europeans. basin model, "said Lia Betti, an anthropologist at the University of Roehampton in London, and lead author of the study. "In predominantly white societies, I imagine that minorities are at greater risk."

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Modern Humans have a narrow pelvis relative to the size of their baby's head.This difference contributes to higher rates of complications during delivery in humans than in other primates.


There is no accepted explanation for why the human pelvis leaves leaves. so little room for delivery. Dr. Betti and his colleague Andrea Manica, of the University of Cambridge, set out to study a highly controversial classical explanation known as the "obstetric dilemma" hypothesis.

This dilemma postulates that the evolution of our species evolved and began to walk upright, the width of the human pelvis narrowing, allowing the body weight to remain closer to its center of gravity. But as humans also developed larger brains, it became more and more difficult for a fetus' skull to sneak through this narrow channel. Betti is skeptical about this explanation and thinks that other possibilities, such as modern diets or the need to support internal organs, might help explain the mismatch between pelvis and fetus.

To explore the idea, she and Dr. Manica measured 348 skeletons from around the world. They found that the shape of the pelvis varied enormously, even more than measurements of the proportion of legs, arms and body that are known to vary significantly between populations. The researchers wrote that it was "remarkable and unexpected".

Most of the time, they discovered that the shape of the pond varied according to the geographical ancestry. People of Sub-Saharan origin generally had the deepest basins at the back, while Native Americans had the widest sides. Europeans, North Africans and Asians have fallen in the middle of the range.

The shape of the genital canal also varies greatly within populations, although the variation decreases as much as a population of African descent. This finding is consistent with others indicating that the genetic diversity of a population decreases as it moves away from the cradle of humanity

The major Part of this variation in pelvic form comes from random fluctuations in gene frequency, although natural selection seems to have played a minor role too, said Dr. Betti. The top of the genital canal is slightly wider in colder climate populations, perhaps to help make the body more stocky.

The variation observed by Dr. Betti suggests that the shape of the pelvis is not so strictly controlled. And if the shape of the pelvis is very variable among populations, it is likely that "the birthing process will be too," said Helen Kurki, professor of anthropology at the University of Victoria at the University of Victoria. Canada.

These findings challenge the idea "" There is a "good" way to bring a baby to life, "said Dr. Kurki, suggesting that a more individualized approach to l & # 39; Childbirth may be preferable.

Although people differ anatomically, Dr. Betti said, his research suggests that these differences are not always functional.

"If you look at the shape of the uterine canal in different people, it might be tempting to think that it is adapted to give birth to babies of heads of different shapes, or something of the kind "

" In fact, the differences are mainly due to chance, which I think is magnificent. Sometimes human variation is just random. "