NHM Wien-science explore how the Mammalian new light tanks can throw on human birth problems

Vienna (OTS) – complications at birth in humans are not uncommon. One reason for this is that the female pelvis is compared to the newborn is relatively narrow. The question of why the female pelvis has not become in the course of Evolution, broad, busy, Anthropologists, and evolutionary biologists for a Long time. One possible reason: A narrow pelvis, and the accompanying strong pelvic floor contribute to the male erection.

Women have a considerably wider pelvis than men. This is seen as an adaptation to the birth of relatively large newborn. Nevertheless, the female pelvis is not so wide that births are always easy. That there is a selection pressure that counteracts an extension of the basin, is therefore considered likely. What is the cause, however, is controversial. For a long time the hypothesis of the so-called „fruit-based Dilemmas,“ was found as the best candidate, according to the upright posture of Homo sapiens requires a narrow pelvis. Empirical evidence there is, however, hardly. An alternative hypothesis represents the pelvic floor in the foreground: A wide pelvis for upright walking human would make attributed to the pelvic floor, the weight of the fetus, as well as the internal organs, prone to incontinence and organ lower (prolapse). Prolapse and incontinence are actually increased in women with a particularly wide pelvis. A Review of such hypotheses is complicated by the limited Variation in terms of anatomy and movement patterns within the modern man considerably.

An international Team, including two researchers belong to the interior of the mammal collection of the natural history Museum of Vienna, has in an online pre-published article (Grunstra et al., American Journal of Human Biology:
https://onlinelibrary.wiley.com/doi/full/10.1002/ajhb.23227) now
a way proposed, in particular the pelvic floor hypothesis based on a comparative basin studies could be further supported. Nicole Grunstra, with the mammal collection of the NHM Vienna associated evolutionary anthropologist and author of the study, looks particularly bats as a success by the end of the study group promise: „bats are the largest in the newborn of all mammals to the world; its weight can be up to 45% of that of the mother. In humans, this value is only about 5%. I noticed that there is a distinct sexual dimorphism in the anatomy of the bat-pool: while in males the pelvis is ossified, the pelvis of the females, without exception, open the birth canal in the first place large enough to give birth to large Young. Bats are the only flying mammals, and most of them rest with the head downwards; both of which are circumstances that reduce the pressure on the pelvic floor.“

This discharge, so the researchers in your article, could would have removed the selection pressure on a narrow pelvis, what is it, females of the Bat – in contrast to the people – in the first place, to open your pelvis and to have such a large newborn. Since there are more than 1,000 bat species differ in their flight and resting behavior, in part considerably, can be precisely made in advance to say: Is the pelvic floor hypothesis is applicable, should erratically have flying, as well as in an upright position in columns, dormant species due to the greater acceleration forces on the pelvic floor less open pelvis in the female gender. This is currently being investigated just by using the extensive mammal collection of the NHM Vienna. Grunstra is convinced that the view beyond the horizon of anthropology promises to new discoveries: „The man is first of all a Mammal, and many of the anatomic challenges that affect him, are to be found also in other groups. A comparative approach, therefore, is certainly an asset.“

The researchers point out that mammals have a total of a wide range of relevant Variation with respect to locomotion, posture, and relative size of the newborn, both with regard to Similarities, as well as what differences to the Situation in humans. Comparative studies on different mammalian groups can help to achieve a evolutionarily less narrow understanding of the birth to the problem of the people.

„For the people,“ explains Frank Zachos, head of the mammal collection at the natural history Museum of Vienna and Co-author of the study, „is also a different possible angle of view thanks to Mihaela Pavličev from Cincinnati, which is also involved in the study: A strong pelvic floor is favored by a narrow pelvis contributes, possibly, to the male erection, a feature of obvious importance for the reproduction, and thus to evolutionary Fitness. So it would be possible that the selection for a narrow pelvis and acts primarily on the male gender, and a widening of the female pelvis is prevented only indirectly.“

Mag. Irina Kubadinow
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Mag. Verena Randolf
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Mag. Magdalena Reuss
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