Look up the term "pelvic canal" in the typical anatomy or obstetrics textbook, and you will probably find a description like this: "Well-built healthy women who had a good diet during their growth period usually have a wide pelvis . "
Such a basin, continues the text, allows" the least difficulty during childbirth "
. But such characterizations have long been based on anatomical studies of people of European descent. In fact, the structure of the pelvic canal, the bony structure through which most of us enter the world, varies according to a recent study in the Proceedings of the Royal Society B.
"What worries me is that doctors come to school from the European model of the EU basin," said Lia Betti, anthropologist at the University of Roehampton in London, and the lead author of the study. "In societies that are mostly white, I would imagine that minorities are more at risk."
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Modern humans have narrow pelvis compared to the size of baby heads. This discrepancy contributes to higher rates of birth complications in humans than in other primates.
Factors such as the time a baby takes to travel through the canal, or which direction the baby's head is at birth, may change depending on the shape of the pelvis. These factors, in turn, could influence decisions about when to begin labor, how to assist with tweezers, or when to deliver by caesarean section. Betti.
There is no accepted explanation for why the human pelvis leaves so little room for childbirth. Dr. Betti and her colleague Andrea Manica from the University of Cambridge began to study a classic, if controversial, explanation known as the "birth dilemma" hypothesis.
The dilemma is that our species evolved and uprighted The width of the human pelvis was narrowed so that body weight could stay closer to its center of gravity. But when humans also developed larger brains, it became more difficult for the skull of a fetus to squeeze through this narrow channel.
Dr. Betti is skeptical of this explanation and believes that other options, such as modern diets or the need to support internal organs, could help explain the disproportion between the pelvis and the fetus.
To explore this idea, they measured and Dr. Manica 348 skeletons from around the world. They found that the pelvic shape varied enormously, even more than the measures of leg, arm, and general body proportions of which is known to vary significantly between populations. That was "remarkable and unexpected," the researchers wrote.
Most of the time they found out that the pelvic shape varied along geographic lineages. Sub-Saharan people generally had the deepest basins from the back to the front, while the Native Americans had the widest side to side. Europeans, North Africans and Asians fell into the middle of the circulation area.
Also, the birth canal form varied widely among the populations, although the variation was the lower the further a population came from Africa. The finding agrees with others, suggesting that the genetic diversity of a population decreases as it moves away from the cradle of humanity  M random fluctuations in gene frequency, although the natural Selection also seems to have played a subordinate role. Betti. The upper part of the birth canal is slightly wider in populations from colder climates, perhaps to support the body Stocker
Betti observed variation suggesting that the pelvic shape is not so tightly controlled. And if the shape of the pelvis is very different across populations, it is likely "that the birth process is also very variable," said Helen Kurki, an anthropology professor at the University of Victoria in Canada.
These findings challenge the idea of a "proper" way to give birth to a baby, "said Dr. Kurki, suggesting that a more personalized approach to childbirth might be better.
Although humans are anatomically different from each other differ, says Dr. Betti, their research suggests that differences are not always functional.
"If you look at the shape of the birth canal in different people, it might be tempting to believe that babies are different shaped heads or something like that, "she said
" In fact, the differences are mostly random, which I think is nice. Sometimes human variation is just random. "