Transportation research part d transport and environment

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This site is a owned and operated by the International Urogynecological Association (IUGA). Tague, Louisiana State University, Baton Rouge, Louisiana, and accepted by the Editorial Board March 25, 2015 (received for review October 24, 2014)Because of the tight fit of the large transportation research part d transport and environment neonate through the narrow maternal birth canal, childbirth is remarkably difficult.

In this study we show that the dimensions of head, stature, and pelvis in a human body are linked in a complex way that was not recognized before and that contributes to ameliorate this tight fit.

We show that females with a large head possess a birth canal that can better accommodate large-headed neonates. Because mothers with large heads usually give birth to neonates with large heads, 100 mg detected pattern transportation research part d transport and environment covariation contributes to ease childbirth and has likely evolved in response to strong selection.

Compared with other primates, childbirth is remarkably difficult in triderm cream because the head of a human neonate is large relative to the birth-relevant dimensions of the maternal pelvis.

It seems puzzling that females have not evolved wider pelvises despite the high maternal mortality and morbidity risk connected to childbirth. Despite this seeming lack of change in average pelvic morphology, we show that humans have evolved a complex link between pelvis shape, stature, and head circumference that was not recognized before. Short females with an increased risk of cephalopelvic mismatch possess a rounder inlet, which is beneficial for obstetrics.

We suggest that these covariances have evolved by the strong correlational selection resulting from childbirth. Childbirth is remarkably difficult in humans because of the tight fit of the human neonate through the maternal birth canal (1, 2). Without effective medical intervention, maternal mortality due to childbirth is estimated to be 1.

In evolutionary terms, there have been incredible fitness costs associated with childbirth in humans throughout modern human evolution, yet the birth canal has not become sufficiently wider. The shape of the human pelvis is assumed to be a compromise solution. The obstetric dilemma might further be aggravated by a higher infant survival rate for heavier neonates (15), implying that a higher birth weight is favored by selection.

However, a recent study showed that neonatal size and human gestation length are limited not only by pelvic dimensions but also by maternal metabolic capacity (16). Despite the effect of environmental factors, pelvic dimensions are highly heritable in human populations (most pelvic traits have heritabilities in the range of 0. It has further been claimed that low levels of integration in the pelvis enable high evolvability (14, 21, 22), yet pelvis shape has seemingly not sufficiently responded to the strong selection pressure imposed by childbirth.

Despite insufficient change in average pelvic morphology, selection might have shaped the covariation between pelvic morphology and other body dimensions to ameliorate the consequences of pelvic constraints on childbirth. A twin study (23) reported a heritability of 0. Because of the considerable heritabilities for head size and pelvic dimensions, we transportation research part d transport and environment that females with a larger head have evolved a birth canal that can better accommodate large-headed neonates, compared with females with a smaller transportation research part d transport and environment, who are likely to give birth to children with smaller heads.

Similarly, the risk of birth complications increases if the father is much taller than the mother (25). A short woman with a small pelvis might give birth to a large neonate with a large head, inherited from a much taller father.

Given the high heritability of stature (24, 31, 32), we therefore also predict that the stronger obstetric selection pressure on shorter women has led to a pelvis with a birth canal that is more shaped toward obstetric demands in comparison with taller women.

We suggest that the optimal compromise between a large birth canal and a narrow pelvis is not uniform across a population but rather depends on both head size and stature. The joint selection regimes might have led to an adaptive integration (covariation) between pelvis shape, head circumference, and stature within human populations. To detect such integration patterns within the human body, we assess the covariation between human pelvis shape, head circumference, and stature in males and females by applying geometric morphometrics to fine-resolution 3D landmark data (Fig.

The full set of 126 3D pelvic landmarks measured on each pelvis, shown as red spheres on the mean pelvis shape, are shown in (A) anterior, (B) superior, and (C) lateral view.

The mean pelvis shape was computed as the average shape of all individuals in our dataset. On average, females had a broader and flatter pelvis with a wider and shallower pelvic cavity than males (Fig.

Sexual dimorphism in the human pelvis. The differences between these two average shapes illustrate well-known patterns of sexual dimorphism in the human pelvis. Females have a broader and flatter pelvis, a wider and shallower pelvic cavity, a wider subpubic angle, and smaller acetabula than males.

Johnson fakes statistics for head circumference and stature are given in Table 1. Pelvis shape was significantly associated with stature in both sexes and with head circumference in transportation research part d transport and environment (Table 2).

Taller individuals had, on average, a transportation research part d transport and environment higher and narrower pelvis with a more oval pelvic inlet and a more forward projecting transportation research part d transport and environment than shorter individuals.

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