Sex differences in the pelvis did not evolve de novo in modern humans

Fischer, Barbara; Grunstra, Nicole D S; Zaffarini, Eva; Mitterœcker, Philipp

doi:10.1038/s41559-021-01425-z

Cited by 16 publications

(27 citation statements)

References 66 publications

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“…In fact, the existence of more pronounced pelvic sex differences in mammals that give birth to relatively large neonates as well as the presence of pelvic dimorphism in species that are monomorphic in body size (e.g. Hisaw, 1924 ; Tague, 2005 , 2016 ; Moffett, 2017 ; Grunstra et al ., 2019 ) may be explained by this potential mechanism (Fischer et al ., 2021 ).…”

Section: Sexual Dimorphismmentioning

confidence: 99%

“…The pattern of sexual dimorphism in the human pelvis is opposite to that in human body size, indicating that pelvic dimorphism is not a simple corollary of the hormone‐driven induction of long bone growth. The magnitude of human pelvic sexual dimorphism is marked when compared to the often much subtler dimorphism in non‐human mammals, including our phylogenetically closest ape relatives (Tague, 2005 ; Fischer et al ., 2021 ). It is therefore unlikely that sex differences in the human pelvis can be explained by the action of sex hormones alone; rather, they are more likely the result of a combination of existing developmental machinery and direct, antagonistic selective forces (Fischer et al ., 2021 ).…”

Section: Sexual Dimorphismmentioning

confidence: 99%

“…In fact, the existence of more pronounced pelvic sex differences in mammals that give birth to relatively large neonates as well as the presence of pelvic dimorphism in species that are monomorphic in body size (e.g. Hisaw, 1924;Tague, 2005Tague, , 2016Moffett, 2017;Grunstra et al, 2019) may be explained by this potential mechanism (Fischer et al, 2021). The pelvic inlet is often rounder in females and more heart-shaped in males, while the distance between the ischial spines is larger in females (arrows).…”

Section: Sexual Dimorphismmentioning

confidence: 99%

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The obstetrical dilemma hypothesis: there's life in the old dog yet

et al. 2021

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The term 'obstetrical dilemma' was coined by Washburn in 1960 to describe the trade-off between selection for a larger birth canal, permitting successful passage of a big-brained human neonate, and the smaller pelvic dimensions required for bipedal locomotion. His suggested solution to these antagonistic pressures was to give birth prematurely, explaining the unusual degree of neurological and physical immaturity, or secondary altriciality, observed in human infants. This proposed trade-off has traditionally been offered as the predominant evolutionary explanation for why human childbirth is so challenging, and inherently risky, compared to that of other primates. This perceived difficulty is likely due to the tight fit of fetal to maternal pelvic dimensions along with the convoluted shape of the birth canal and a comparatively low degree of ligamentous flexibility. Although the ideas combined under the obstetrical dilemma hypothesis originated almost a century ago, they have received renewed attention and empirical scrutiny in the last decade, with some researchers advocating complete rejection of the hypothesis and its assumptions. However, the hypothesis is complex because it presently captures several, mutually non-exclusive ideas: (i) there is an evolutionary trade-off resulting from opposing selection pressures on the pelvis; (ii) selection favouring a narrow pelvis specifically derives from bipedalism; (iii) human neonates are secondarily altricial because they are born relatively immature to ensure that they fit through the maternal bony pelvis; (iv) as a corollary to the asymmetric selection pressure for a spacious birth canal in females, humans evolved pronounced sexual dimorphism of pelvic shape. Recently, the hypothesis has been challenged on both empirical and theoretical grounds. Here, we appraise the original ideas captured under the 'obstetrical dilemma' and their subsequent evolution. We also evaluate complementary and alternative explanations for a tight fetopelvic fit and obstructed labour, including ecological factors related to nutrition and thermoregulation, constraints imposed by the stability of the pelvic floor or by maternal and fetal metabolism, the energetics of bipedalism, and variability in pelvic shape. This reveals that human childbirth is affected by a complex combination of evolutionary, ecological, and biocultural factors, which variably constrain maternal pelvic form and fetal growth. Our review demonstrates that it is unwarranted to reject the obstetrical dilemma hypothesis entirely because several of its fundamental assumptions have not been successfully discounted despite claims to the contrary. As such, the obstetrical dilemma remains a tenable hypothesis that can be used productively to guide evolutionary research.

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Section: Sexual Dimorphismmentioning

confidence: 99%

Section: Sexual Dimorphismmentioning

confidence: 99%

“…In fact, the existence of more pronounced pelvic sex differences in mammals that give birth to relatively large neonates as well as the presence of pelvic dimorphism in species that are monomorphic in body size (e.g. Hisaw, 1924;Tague, 2005Tague, , 2016Moffett, 2017;Grunstra et al, 2019) may be explained by this potential mechanism (Fischer et al, 2021). The pelvic inlet is often rounder in females and more heart-shaped in males, while the distance between the ischial spines is larger in females (arrows).…”

Section: Sexual Dimorphismmentioning

confidence: 99%

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The obstetrical dilemma hypothesis: there's life in the old dog yet

et al. 2021

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“…Pelvic features can be first seen in teenagers (Rebay‐Salisbury et al, 2018; Waltenberger, Rebay‐Salisbury, & Mitteroecker, 2021) and increase in expression during the reproductive period. In this period, pelvic shape also remodels to a more gynecoid pelvis, presumably due to increased estrogen production during pregnancy (Fischer et al, 2021; Fischer & Mitteroecker, 2017; Huseynov et al, 2016; Kjeldsen et al, 2021; Waltenberger, Rebay‐Salisbury, & Mitteroecker, 2021).…”

Section: Discussionmentioning

confidence: 99%

Are parturition scars truly signs of birth? The estimation of parity in a well‐documented modern sample

Waltenberger

Rebay‐Salisbury

Mitterœcker

2022

Intl J of Osteoarchaeology

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Parturition scars have been frequently studied in the last decades, but their association with pregnancy and birth is still controversial. Other biomechanical, biometric, and lifestyle factors are also likely to influence the development of pelvic features. Most previous studies of pelvic features were based on skeletal collections with no reliable information on parity or even sex and thus were unable to disentangle these factors. Here, we study the association of pelvic features with birth and other body variables (age, stature, weight, osteoarthritis, and centrum–collum–diaphyseal angle) using multiple regression and path modeling in a modern sample of female individuals from New Mexico (USA) with detailed background information (n = 150). We also explored the utility of pelvic features to predict the number of births. To this end, we scored the expression of the preauricular sulcus, sacral preauricular extension, extended pubic tubercle, exostosis at the pectineal line, dorsal, and ventral pubic pitting using CT scans from the New Mexico Decedent Image Database. Quantitative measurements of pelvic features were then used as predictors of parity. Overall, the regression models accounted only for relatively small fractions of variance in pelvic feature expression. The only feature significantly associated with the number of births was dorsal pubic pitting (R2 = 0.2372), whereas the expression of most pelvic features increased with age, independent of parity. Presumably, the development of dorsal pubic pitting is affected both by biomechanical stress and the increased hormonal secretion during pregnancy and birth. The individual prediction of parity based on pelvic features is too imprecise for forensic or archeological applications. However, using a size score of dorsal pubic pitting allowed us to estimate the mean parity in groups of individuals relatively well. Hence, pelvic features may still be used to compare average parity across recent or historic populations.

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“…Various parameters of pelvis essential for sex determination are discussed in this paper. A progressive evolutionary change can be observed in the magnitude of the pelvic sex differences in modern humans but the pattern of sexual dimorphism has not evolved in modern beings and must have been present in the ancestors of man [19]. Parameters such as weight and roughness of the bones involved, os coxae shape, pelvic brim, pelvic inlet, greater sciatic notch, acetabular fossa position, periauricular sulcus, ischial tuberosity, sub-pubic angle, sub-pubic concavity, shape of obturator foramen, shape of sacral body etc.…”

Section: Introductionmentioning

confidence: 99%

Sex Determination by Pelvis: A Mini Literature Review

Joon¹,

Rohatgi²

2022

IJRASET

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An endeavor involving the application of physical anthropology in the context of civil or criminal cases is forensic anthropology. Determination of sex is the matter of absolute attention for a forensic anthropologist as it is the first step towards positive identification process after discovering the skeletal or bone remains of human origin. Pelvic Girdle is the most sexually dimorphic part of human skeleton which estimates the result with an accuracy of 95% and along with sacrum i.e. pelvis it estimates the sex with 98% accuracy and it decomposes slowly than other parts. Sex can be estimated by skeletal remains only in adults as the marked variations on bones be in terms of morphology or size are visible only after attaining puberty. Methods involved in sex estimation process are Morphological, Metric and Radiological. The Morphological method accords the result by considering the morphological sexual traits on pelvis and in contrary the Metric method involves measurement of bones and indices. Metric recipe should be applied in combination with Morphological results as Morphometric in order to get more accurate results. Whereas, in radiological recipe radiographs of collected remains are taken from which certain measurements and morphologic observations can be carried out. Quantitative and statistical analysis can be done using these mentioned methods. Skeletal features may vary with population. Bones are very frail in nature so, in turn, cannot be collected fully thus when fragmented remains are collected the morphometric method is of ultimate importance in the estimation process.

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Sex differences in the pelvis did not evolve de novo in modern humans

Cited by 16 publications

References 66 publications

The obstetrical dilemma hypothesis: there's life in the old dog yet

The obstetrical dilemma hypothesis: there's life in the old dog yet

Are parturition scars truly signs of birth? The estimation of parity in a well‐documented modern sample

Sex Determination by Pelvis: A Mini Literature Review

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