scholarly journals Human variation in the shape of the birth canal is significant and geographically structured

2018 ◽  
Vol 285 (1889) ◽  
pp. 20181807 ◽  
Author(s):  
Lia Betti ◽  
Andrea Manica
Keyword(s):  
Morphological Diversity ◽  
Neutral Evolution ◽  
Human Populations ◽  
Shape Variation ◽  
Birth Canal ◽  
Neutral Genetic Diversity ◽  
A Minor ◽  
Human Birth ◽  
European Women ◽  
Oval Shape

The human birth canal shows a tight fit with the size of the neonate, which can lead to obstetric complications. This is not the case in other apes, and has been explained as the outcome of conflicting evolutionary pressures for bipedal locomotion and parturition of a highly encephalized fetus. Despite the suggested evolutionary constraints on the female pelvis, we show that women are, in fact, extremely variable in the shape of the bony birth canal, with human populations having differently shaped pelvic canals. Neutral evolution through genetic drift and differential migration are largely responsible for the observed pattern of morphological diversity, which correlates well with neutral genetic diversity. Climatic adaptation might have played a role, albeit a minor one, with populations from colder regions showing a more transversally oval shape of the canal inlet. The significant extent of canal shape variation among women from different regions of the world has important implications for modern obstetric practice in multi-ethnic societies, as modern medical understanding has been largely developed on studies of European women.

scholarly journals Shaping birth: variation in the birth canal and the importance of inclusive obstetric care

2021 ◽  
Vol 376 (1827) ◽  
Author(s):  
Lia Betti
Keyword(s):  
White Women ◽  
Obstetric Care ◽  
European Ancestry ◽  
Human Populations ◽  
Maternal Child Health ◽  
Birth Canal ◽  
Pelvic Morphology ◽  
Pelvic Shape ◽  
Training Need ◽  
Human Birth

Regional variation in pelvic morphology and childbirth has long occurred alongside traditional labour support and an understanding of possible normal courses of childbirth for each population. The process of migration and globalization has broken down these links, while a European model of ‘normal’ labour has become widespread. The description of ‘normal’ childbirth provided within obstetrics and midwifery textbooks, in fact, is modelled on a specific pelvic morphology that is common in European women. There is mounting evidence, however, that this model is not representative of women's diversity, especially for women of non-white ethnicities. The human birth canal is very variable in shape, both within and among human populations, and differences in pelvic shapes have been associated with differences in the mechanism of labour. Normalizing a white-centred model of female anatomy and of childbirth can disadvantage women of non-European ancestry. Because they are less likely to fit within this model, pelvic shape and labour pattern in non-white women are more likely to be considered ‘abnormal’, potentially leading to increased rates of labour intervention. To ensure that maternal care is inclusive and as safe as possible for all women, obstetric and midwifery training need to incorporate women's diversity. This article is part of the theme issue ‘Multidisciplinary perspectives on social support and maternal–child health’.

Shell variations in the gastropod, Monodonta labio, in the North-western Pacific: the important role of temperature in the evolution process

2019 ◽  
Vol 99 (7) ◽  
pp. 1591-1599
Author(s):  
Dan Zhao ◽  
Ling-Feng Kong ◽  
Takenori Sasaki ◽  
Qi Li
Keyword(s):  
Environmental Gradients ◽  
Ecological Factors ◽  
Local Maximum ◽  
Morphological Diversity ◽  
Shell Shape ◽  
Shape Variation ◽  
Genetic Structuring ◽  
Morphological Variations ◽  
China Sea

AbstractMolluscan shells showing phenotypic variations are ideal models for studying evolution and plasticity. In north-eastern Asia, genetic and morphological diversity of the gastropod, Monodonta labio, were assumed to be influenced by both palaeoclimatic changes and current ecological factors. In this study, we examined spatial variations in shell shape of M. labio using general measurement and geometric morphometric analysis. We also investigated whether shell shape variation is best explained by environmental gradients or by genetic structuring, based on our prior molecular phylogeographic study. Two common morphological forms were observed among Chinese populations and in the adjacent Asian areas. Both the analyses revealed separation patterns in morphological variations of shell shape among the clades and populations. Environmental modelling analysis showed a significant correlation between shape variations and local maximum temperatures of the warmest month, indicating the role of natural selection in the evolution of this species. Data obtained in this study, combined with the cytochrome oxidase subunit I (COI) molecular phylogenetic data from the prior study, showed that morphological variations in M. labio were constrained by both local adaptation and phenotypic plasticity. We hypothesized that geographic separation by the Dongshan Landbridge was the first step towards its diversification, and that the temperature gradient between the East China Sea and South China Sea probably was the selective force driving the divergence of its morphological variations.

Morphological diversity of wild rabbit populations: implications for archaeology and palaeontology

2019 ◽  
Vol 128 (1) ◽  
pp. 211-224 ◽  
Author(s):  
Maxime Pelletier
Keyword(s):  
Sexual Dimorphism ◽  
Western Europe ◽  
Geographical Location ◽  
Morphological Diversity ◽  
Population Level ◽  
European Rabbit ◽  
Wild Rabbit ◽  
Shape Variation ◽  
Hunting Behaviour ◽  
Behavioural Aspects

Abstract Morphometric characteristics of the European rabbit (Oryctolagus cuniculus) are regularly used in archaeological and palaeontological studies to explore aspects of prehistoric human hunting behaviour, to reconstruct past environments or to define new species. However, the variability of these characteristics is still both poorly understood and under-documented due to a lack of population-level data that are essential for reliably interpreting the fossil record of this species. Here we address the morphometric diversity of wild rabbits in seven current populations from south-western Europe. Size variations in different skeletal parts were analysed to explore the potential impact of sexual dimorphism. A geometric morphometric analysis of the third lower premolar (p3) – a tooth commonly used to distinguish leporid species – was used to evaluate the relative effects of size, phylogeny, geographical location and climate on shape variation. The results show a negligible impact of sexual dimorphism, contradicting previous studies. We also demonstrate geography and climate to be the main factors driving variation in p3 shape, potentially calling into question criteria typically used to identify rabbit species. These results are valuable not only for palaeobiologists studying the taxonomy and the evolutionary history of the leporid family but also for archaeologists interested in the socio-economic and behavioural aspects of Palaeolithic human groups.

scholarly journals Signatures of genetic variation in human microRNAs point to processes of positive selection related to population-specific disease risks

2021 ◽  
Author(s):  
Pablo Villegas Mirón ◽  
Alicia Gallego ◽  
Jaume Bertranpetit ◽  
Hafid Laayouni ◽  
Yolanda Espinosa-Parrilla
Keyword(s):  
Genetic Variation ◽  
Disease Risk ◽  
In Silico Analysis ◽  
Human Populations ◽  
Evolutionary Constraint ◽  
Seed Region ◽  
Specific Disease ◽  
A Minor ◽  
Diversity Profiles

The occurrence of natural variation in human microRNAs has been the focus of numerous studies during the last twenty years. Most of them have been dedicated to study the role of specific mutations in diseases, like cancer, while a minor fraction seek to analyse the diversity profiles of microRNAs in the genomes of human populations. In the present study we analyse the latest human microRNA annotations in the light of the most updated catalog of genetic variation provided by the 1000 Genomes Project. We show by means of the in silico analysis of noncoding variation of microRNAs that the level of evolutionary constraint of these sequences is governed by the interplay of different factors, like their evolutionary age or the genomic location where they emerged. The role of mutations in the shaping of microRNA-driven regulatory interactions is emphasized with the acknowledgement that, while the whole microRNA sequence is highly conserved, the seed region shows a pattern of higher genetic diversity that appears to be caused by the dramatic frequency shifts of a fraction of human microRNAs. We highlight the participation of these microRNAs in population-specific processes by identifying that not only the seed, but also the loop, are particularly differentiated regions among human populations. The quantitative computational comparison of signatures of population differentiation showed that candidate microRNAs with the largest differences are enriched in variants implicated in gene expression levels (eQTLs), selective sweeps and pathological processes. We explore the implication of these evolutionary-driven microRNAs and their SNPs in human diseases, such as different types of cancer, and discuss their role in population-specific disease risk.

scholarly journals How and why patterns of sexual dimorphism in human faces vary across the world

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Karel Kleisner ◽  
Petr Tureček ◽  
S. Craig Roberts ◽  
Jan Havlíček ◽  
Jaroslava Varella Valentova ◽  
...  
Keyword(s):  
Sexual Selection ◽  
Sexual Dimorphism ◽  
Mate Choice ◽  
Body Height ◽  
Human Populations ◽  
Sexually Dimorphic ◽  
Shape Variation ◽  
Cross Cultural Differences ◽  
Facial Shape ◽  
Human Faces

AbstractSexual selection, including mate choice and intrasexual competition, is responsible for the evolution of some of the most elaborated and sexually dimorphic traits in animals. Although there is sexual dimorphism in the shape of human faces, it is not clear whether this is similarly due to mate choice, or whether mate choice affects only part of the facial shape difference between men and women. Here we explore these questions by investigating patterns of both facial shape and facial preference across a diverse set of human populations. We find evidence that human populations vary substantially and unexpectedly in both the magnitude and direction of facial sexually dimorphic traits. In particular, European and South American populations display larger levels of facial sexual dimorphism than African populations. Neither cross-cultural differences in facial shape variation, sex differences in body height, nor differing preferences for facial femininity and masculinity across countries, explain the observed patterns of facial dimorphism. Altogether, the association between sexual shape dimorphism and attractiveness is moderate for women and weak (or absent) for men. Analysis that distinguishes between allometric and non-allometric components reveals that non-allometric facial dimorphism is preferred in women’s faces but not in faces of men. This might be due to different regimes of ongoing sexual selection acting on men, such as stronger intersexual selection for body height and more intense intrasexual physical competition, compared with women.

scholarly journals The evolution of pelvic canal shape and rotational birth in humans

BMC Biology ◽  
2021 ◽  
Vol 19 (1) ◽  
Author(s):  
Ekaterina Stansfield ◽  
Barbara Fischer ◽  
Nicole D. S. Grunstra ◽  
Maria Villa Pouca ◽  
Philipp Mitteroecker
Keyword(s):  
Pelvic Floor ◽  
Complex Shape ◽  
Upright Posture ◽  
Birth Canal ◽  
Abdominal Organs ◽  
Pelvic Inlet ◽  
Deformation Stress ◽  
The Stability ◽  
Floor Stability ◽  
Oval Shape

Abstract Background The human foetus typically needs to rotate when passing through the tight birth canal because of the complex shape of the pelvis. In most women, the upper part, or inlet, of the birth canal has a round or mediolaterally oval shape, which is considered ideal for parturition, but it is unknown why the lower part of the birth canal has a pronounced anteroposteriorly oval shape. Results Here, we show that the shape of the lower birth canal affects the ability of the pelvic floor to resist the pressure exerted by the abdominal organs and the foetus. Based on a series of finite element analyses, we found that the highest deformation, stress, and strain occur in pelvic floors with a circular or mediolaterally oval shape, whereas an anteroposterior elongation increases pelvic floor stability. Conclusions This suggests that the anteroposterior oval outlet shape is an evolutionary adaptation for pelvic floor support. For the pelvic inlet, by contrast, it has long been assumed that the mediolateral dimension is constrained by the efficiency of upright locomotion. But we argue that the mediolateral elongation has evolved because of the limits on the anteroposterior diameter imposed by upright posture. We show that an anteroposteriorly deeper inlet would require greater pelvic tilt and lumbar lordosis, which compromises spine health and the stability of upright posture. These different requirements of the pelvic inlet and outlet likely have led to the complex shape of the pelvic canal and to the evolution of rotational birth characteristic of humans.

scholarly journals Genome scans of facial features in East Africans and cross-population comparisons reveal novel associations

PLoS Genetics ◽  
2021 ◽  
Vol 17 (8) ◽  
pp. e1009695
Author(s):  
Chenxing Liu ◽  
Myoung Keun Lee ◽  
Sahin Naqvi ◽  
Hanne Hoskens ◽  
Dongjing Liu ◽  
...  
Keyword(s):  
Genetic Basis ◽  
Human Populations ◽  
Facial Morphology ◽  
Shape Variation ◽  
East African ◽  
Enhancer Activity ◽  
Genome Scans ◽  
Multiple Phenotypes ◽  
Population Comparisons ◽  
Cranial Neural Crest Cells

Facial morphology is highly variable, both within and among human populations, and a sizable portion of this variation is attributable to genetics. Previous genome scans have revealed more than 100 genetic loci associated with different aspects of normal-range facial variation. Most of these loci have been detected in Europeans, with few studies focusing on other ancestral groups. Consequently, the degree to which facial traits share a common genetic basis across diverse sets of humans remains largely unknown. We therefore investigated the genetic basis of facial morphology in an East African cohort. We applied an open-ended data-driven phenotyping approach to a sample of 2,595 3D facial images collected on Tanzanian children. This approach segments the face into hierarchically arranged, multivariate features that capture the shape variation after adjusting for age, sex, height, weight, facial size and population stratification. Genome scans of these multivariate shape phenotypes revealed significant (p < 2.5 × 10−8) signals at 20 loci, which were enriched for active chromatin elements in human cranial neural crest cells and embryonic craniofacial tissue, consistent with an early developmental origin of the facial variation. Two of these associations were in highly conserved regions showing craniofacial-specific enhancer activity during embryological development (5q31.1 and 12q21.31). Six of the 20 loci surpassed a stricter threshold accounting for multiple phenotypes with study-wide significance (p < 6.25 × 10−10). Cross-population comparisons indicated 10 association signals were shared with Europeans (seven sharing the same associated SNP), and facilitated fine-mapping of causal variants at previously reported loci. Taken together, these results may point to both shared and population-specific components to the genetic architecture of facial variation.

scholarly journals Ontogenetic and static allometry in the skull and cranial units of nine-banded armadillos (Cingulata: Dasypodidae: Dasypus novemcinctus)

2020 ◽  
Vol 131 (3) ◽  
pp. 673-698
Author(s):  
Kévin Le Verger ◽  
Lionel Hautier ◽  
Jérémie Bardin ◽  
Sylvain Gerber ◽  
Frédéric Delsuc ◽  
...  
Keyword(s):  
Developmental Stages ◽  
Morphological Evolution ◽  
Morphological Diversity ◽  
Shape Variation ◽  
Dasypus Novemcinctus ◽  
Global Pattern ◽  
Geometric Morphometric ◽  
Multi Scale ◽  
Infraorbital Canal ◽  
Row Reduction

Abstract A large part of extant and past mammalian morphological diversity is related to variation in size through allometric effects. Previous studies suggested that craniofacial allometry is the dominant pattern underlying mammalian skull shape variation, but cranial allometries were rarely characterized within cranial units such as individual bones. Here, we used 3D geometric morphometric methods to study allometric patterns of the whole skull (global) and of cranial units (local) in a postnatal developmental series of nine-banded armadillos (Dasypus novemcinctus ssp.). Analyses were conducted at the ontogenetic and static levels, and for successive developmental stages. Our results support craniofacial allometry as the global pattern along with more local allometric trends, such as the relative posterior elongation of the infraorbital canal, the tooth row reduction on the maxillary, and the marked development of nuchal crests on the supraoccipital with increasing skull size. Our study also reports allometric proportions of shape variation varying substantially among cranial units and across ontogenetic stages. The multi-scale approach advocated here allowed unveiling previously unnoticed allometric variations, indicating an untapped complexity of cranial allometric patterns to further explain mammalian morphological evolution.

scholarly journals Local superimpositions facilitate morphometric analysis of complex articulating structures

2021 ◽  
Author(s):  
Daniel Rhoda ◽  
Marion Segall ◽  
Olivier Larouche ◽  
Kory Evans ◽  
Kenneth D Angielczyk
Keyword(s):  
Morphometric Analysis ◽  
Morphological Diversity ◽  
The Body ◽  
Shape Variation ◽  
Geometric Morphometric ◽  
Positional Variation ◽  
Biological Form ◽  
Biological Interpretation ◽  
Data Capturing ◽  
Vertebrate Skeleton

Abstract Articulating structures, such as the vertebrate skeleton or the body and limb segments of the arthropod exoskeleton, comprise a majority of the morphological diversity across the eukaryotic tree of life. Quantifying the form of articulating structures is therefore imperative for a fuller understanding of the factors influencing biological form. A wealth of freely available 3 D data capturing this morphological diversity is stored in online repositories such as Morphosource, but the geometric morphometric analysis of an articulating structure is impeded by arbitrary differences in the resting positions of its individual articulating elements. In complex articulating structures, where the angles between articulating elements cannot be standardized, landmarks on articulating elements must be Procrustes superimposed independently (locally) and then recombined to quantify variation in the entire articulating structure simultaneously. Here, we discuss recent advances in local superimposition techniques, namely the ‘matched local superimpositions’ approach which incorporates anatomically-accurate relative sizes, positions, and orientations of locally-superimposed landmarks, enabling clearer biological interpretation. We also use simulations to evaluate the consequences of choice of superimposition approach. Our results show that local superimpositions will isolate shape variation within locally-superimposed landmark subsets by sacrificing size and positional variation. They may also create morphometric ‘modules’ when there are none by increasing integration within the locally-superimposed subsets, however this effect is no greater than the spurious between-module integration created when superimposing landmark subsets (i.e., articulating elements) together. Taken together, our results show that local superimposition techniques differ from conventional Procrustes superimpositions in predictable ways. Finally, we use empirical datasets of the skulls of wrasses and colubriform snakes to highlight the promise of local superimpositions and their utility. Complex articulating structures must be studied, and the only current solution to do so is local superimpositions.

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