Why can textbooks need to update what they say about birth channels

TrilobitesA new study shows that the structure of the human pelvis varies from one population to another, which could have consequences on the birth pattern of babies. ImageA comparison of two human basins: the summit is more oval shaped, representing Europeans, North Africans and Amerindians. The background is more circular, representing Africans and Asians from sub-Saharan Africa.CreditCreditLia BettiSearch for the term "pelvic canal" in the typical anatomy or obstetrics textbook, and you will probably find a description like this: had a good diet during the growing period of their childhood, usually have a large pelvis. Such a basin, continues the text, allows "the least possible difficulties during childbirth". But these characterizations have long been based on anatomical studies of people of European descent. . In fact, 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 The findings have implications for how obstetricians treat patients of color, say the authors. In the United States, for example, the risk of death from pregnancy is three to four times higher for black women than for white women. "What worries me is that doctors are coming out of school thinking about the European basin model." Lia Betti, 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."[Like the Science Times page on Facebook. | Sign up for the Science Times newsletter.]Modern humans have a narrow pelvis in relation to the size of the babies' heads. This difference contributes to higher rates of complications during delivery in humans than in other primates. Factors such as the time it takes for a baby to progress through the canal or the direction taken by the head at the time of delivery may change depending on the shape of the pelvis. These factors, in turn, could influence decisions about when to induce labor, how to help forceps or at the time of caesarean delivery, said Dr. Betti. There is no accepted explanation for why the human pool leaves as little room for birth. Dr. Betti and her colleague Andrea Manica of Cambridge University have begun to examine a well-contested classical explanation called the "obstetric dilemma". This dilemma postulates that when our species evolved and began to walk the human pelvis narrowed, allowing the body weight to stay closer to its center of gravity. But as humans also developed larger brains, it was increasingly 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 imbalance between pelvis and fetus. To explore the idea, she and Dr. Manica have 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 chain. The shape of the birth canal has also varied markedly within populations, although this variation has declined further in the case of a population originating from Africa. This finding is consistent with others that indicate that the genetic diversity of a population decreases as it moves away from the cradle of humanity. Most of this variation in pelvic form is due to random fluctuations in gene frequency, although natural selection appears to have also played a minor role. Said Betti. The top of the birth canal is slightly wider in colder climates, perhaps to help make the body more dense. The variation observed by Dr. Betti suggests that the shape of the pelvis is not as 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 results challenge the idea that "there is only one right. Dr. Kurki said, "One way to birth a baby, suggests a more individualized approach to childbirth. Although people differ anatomically, Dr. Betti pointed out that their differences are not always functional. "If you look at the shape of the birth canal in different people, it might be tempting to think that it's suitable for giving birth to babies with heads of different shapes, or something like that," he said. she said. "In fact, the differences are mostly by chance, which seems beautiful to me.Sometimes human variation is just random." Previous reports on human evolution
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