Skeletal variability in the pelvis and limb skeleton of humans: Does stabilizing selection limit female pelvic variation?

Kurki, Helen K.

doi:10.1002/ajhb.22455

Cited by 59 publications

(70 citation statements)

References 45 publications

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“…Accordingly, we hypothesized that correlational selection has produced patterns of covariance between pelvis shape and other body dimensions. Earlier studies based on smaller sets of linear measurements could not clearly demonstrate such patterns (37)(38)(39)(40).…”

Section: Fig 2 Sexual Dimorphism In the Human Pelvis (A)mentioning

confidence: 79%

Covariation between human pelvis shape, stature, and head size alleviates the obstetric dilemma

Fischer

Mitterœcker

2015

Proc. Natl. Acad. Sci. U.S.A.

101

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Compared with other primates, childbirth is remarkably difficult in humans 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. The identified covariance patterns contribute to ameliorate the "obstetric dilemma." Females with a large head, who are likely to give birth to neonates with a large head, possess birth canals that are shaped to better accommodate large-headed neonates. 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. Although males are not subject to obstetric selection, they also show part of these association patterns, indicating a genetic-developmental origin of integration.

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Section: Fig 2 Sexual Dimorphism In the Human Pelvis (A)mentioning

confidence: 79%

Covariation between human pelvis shape, stature, and head size alleviates the obstetric dilemma

Fischer

Mitterœcker

2015

Proc. Natl. Acad. Sci. U.S.A.

101

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“…In relation to the obstetric dilemma, he suggested that such constraints may have reduced the overall evolvability of the birth canal in earlier hominins, but that these constraints became weaker in later hominins. A study of regional skeletal variability in recent human populations found that the pelvic canal was, in fact, the most variable trait, suggesting that stabilizing selection is no longer a major constraint [36].…”

Section: Resolution Of the Dilemma By Genetic Adaptationmentioning

confidence: 99%

Between Scylla and Charybdis: renegotiating resolution of the ‘obstetric dilemma’ in response to ecological change

Wells¹

2015

Phil. Trans. R. Soc. B

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Hominin evolution saw the emergence of two traits-bipedality and encephalization-that are fundamentally linked because the fetal head must pass through the maternal pelvis at birth, a scenario termed the 'obstetric dilemma'. While adaptive explanations for bipedality and large brains address adult phenotype, it is brain and pelvic growth that are subject to the obstetric dilemma. Many contemporary populations experience substantial maternal and perinatal morbidity/mortality from obstructed labour, yet there is increasing recognition that the obstetric dilemma is not fixed and is affected by ecological change. Ecological trends may affect growth of the pelvis and offspring brain to different extents, while the two traits also differ by a generation in the timing of their exposure. Two key questions arise: how can the fit between the maternal pelvis and the offspring brain be 'renegotiated' as the environment changes, and what nutritional signals regulate this process? I argue that the potential for maternal size to change across generations precludes birthweight being under strong genetic influence. Instead, fetal growth tracks maternal phenotype, which buffers short-term ecological perturbations. Nevertheless, rapid changes in nutritional supply between generations can generate antagonistic influences on maternal and offspring traits, increasing the risk of obstructed labour.

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“…A human infant's head enters the inlet facing laterally, and then rotates, usually to face backwards, as it exits through the more anteroposteriorly oriented outlet (figure 2). Although the precise orientation of the infant may vary depending on variations in the shape of the maternal birth canal, this rotation during birth is consistent among humans [4]. In contrast with an ape baby, who passes through the outlet posteriorly between the ischial tuberosities, a human baby emerges more anteriorly, under the ischiopubic rami, owing to the inferior position of the sacrum [33,35].…”

Section: Pelvic Morphology In Humans and Nonhuman Primatesmentioning

confidence: 99%

“…Each of these processes is essential enough to survival and reproductive success as to be under strong pressure from natural selection [1][2][3][4]. As a result, the fossil record of the evolution of the human pelvis over the past 4.5 Myr reveals a profound story concerning selective priorities during different phases of human evolution, and elucidates the essential constraints that formed our modern anatomical condition.…”

Section: Introductionmentioning

confidence: 99%

“…3 Although other hominin species are known from as early as 6 -7 Ma [49][50][51], nothing is known about their pelvic morphology, because no fossil pelvic material has been recovered. 4 In the following discussion, we refer to the humans that succeed H. erectus and predate the Neanderthals, sometimes referred to as 'Archaic Homo sapiens', as Homo heidelbergensis, regardless of their geographical origin. We acknowledge that there is a great deal of disagreement regarding Middle Pleistocene human phylogenetics, and we use this nomenclature not to take a taxonomic position but to clarify discussion.…”

Section: The Evolution Of the Modern Human Pelvismentioning

confidence: 99%

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The evolution of the human pelvis: changing adaptations to bipedalism, obstetrics and thermoregulation

Gruss

Schmitt

2015

Phil. Trans. R. Soc. B

145

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The fossil record of the human pelvis reveals the selective priorities acting on hominin anatomy at different points in our evolutionary history, during which mechanical requirements for locomotion, childbirth and thermoregulation often conflicted. In our earliest upright ancestors, fundamental alterations of the pelvis compared with non-human primates facilitated bipedal walking. Further changes early in hominin evolution produced a platypelloid birth canal in a pelvis that was wide overall, with flaring ilia. This pelvic form was maintained over 3-4 Myr with only moderate changes in response to greater habitat diversity, changes in locomotor behaviour and increases in brain size. It was not until Homo sapiens evolved in Africa and the Middle East 200 000 years ago that the narrow anatomically modern pelvis with a more circular birth canal emerged. This major change appears to reflect selective pressures for further increases in neonatal brain size and for a narrow body shape associated with heat dissipation in warm environments. The advent of the modern birth canal, the shape and alignment of which require fetal rotation during birth, allowed the earliest members of our species to deal obstetrically with increases in encephalization while maintaining a narrow body to meet thermoregulatory demands and enhance locomotor performance.

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Skeletal variability in the pelvis and limb skeleton of humans: Does stabilizing selection limit female pelvic variation?

Abstract: The results suggest that stabilizing selection does not limit variability in the female pelvic canal. Biological plasticity may be greater in the canal than that in other skeletal regions.

Cited by 59 publications

References 45 publications

Covariation between human pelvis shape, stature, and head size alleviates the obstetric dilemma

Covariation between human pelvis shape, stature, and head size alleviates the obstetric dilemma

Between Scylla and Charybdis: renegotiating resolution of the ‘obstetric dilemma’ in response to ecological change

The evolution of the human pelvis: changing adaptations to bipedalism, obstetrics and thermoregulation

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