Obstetrical Constraints and the Origin of Extended Postnatal Brain Maturation in Hominin Evolution

The origin of difficult birth is still a matter of debate in obstetrics. Recent studies hypothesized that early hominins already experienced obstructed labor even with reduced neonatal head sizes. The aim of this work is to test this hypothesis using an extant obstetrical sample with known delivery outcomes. Three delivery outcomes (i.e., instrument-assisted, Caesarean section, and vaginal birth) were evaluated using a discriminant analysis based on 131 mother–baby dyads and 36 feto-pelvic variables. This obstetrical sample was compared with 20 australopithecine “dyads” generated from the combination of six pelvic reconstructions (three for Australopithecus afarensis, two for A. africanus, and one for A. sediba) and three fetal head size estimations. The obstetrical analysis revealed that dystocic births can be predicted by pelvic features such as an anteroposteriorly flattened pelvic inlet. Australopithecines shared these pelvic morphologies with humans and had eutocic birth only for infants of 110 g brain size or smaller, equaling a human-like neonatal/adult brain size ratio of 25–28%. Although birth mechanism cannot be deduced, the newborn/adult brain size ratio was likely more human-like than previously thought, suggesting that australopithecines were secondarily altricial to circumvent instances of obstructed labor and subsequently require a prolonged postnatal brain growth period, implying some aspects of life history pattern similar to modern humans

Dynamic finite-element simulations reveal early origin of complex human birth pattern

Human infants are born neurologically immature, potentially owing to conflicting selection pressures between bipedal locomotion and encephalization as suggested by the obstetrical dilemma hypothesis. Australopithecines are ideal for investigating this trade-off, having a bipedally adapted pelvis, yet relatively small brains. Our finite-element birth simulations indicate that rotational birth cannot be inferred from bony morphology alone. Based on a range of pelvic reconstructions and fetal head sizes, our simulations further imply that australopithecines, like humans, gave birth to immature, secondary altricial newborns with head sizes smaller than those predicted for non-human primates of the same body size especially when soft tissue thickness is adequately approximated. We conclude that australopithecines required cooperative breeding to care for their secondary altricial infants. These prerequisites for advanced cognitive development therefore seem to have been corollary to skeletal adaptations for bipedal locomotion that preceded the appearance of the genus Homo and the increase in encephalization

Author Correction: Dynamic finite-element simulations reveal early origin of complex human birth pattern

Human infants are born neurologically immature, potentially owing to conflicting selection pressures between bipedal locomotion and encephalization as suggested by the obstetrical dilemma hypothesis. Australopithecines are ideal for investigating this trade-off, having a bipedally adapted pelvis, yet relatively small brains. Our finite-element birth simulations indicate that rotational birth cannot be inferred from bony morphology alone. Based on a range of pelvic reconstructions and fetal head sizes, our simulations further imply that australopithecines, like humans, gave birth to immature, secondary altricial newborns with head sizes smaller than those predicted for non-human primates of the same body size especially when soft tissue thickness is adequately approximated. We conclude that australopithecines required cooperative breeding to care for their secondary altricial infants. These prerequisites for advanced cognitive development therefore seem to have been corollary to skeletal adaptations for bipedal locomotion that preceded the appearance of the genus Homo and the increase in encephalization

Evolution of birth process in human lineage. Assessment of fetal-pelvic constrain with to complementary methods : virtual birth simulation and discriminant analysis of delivery groups in an obstetrical sample

Notre objectif est d’étudier les modalités d’accouchement au sein de la lignée humaine. Pour cela, nous utilisons deux approches complémentaires : la simulation numérique de l’accouchement et l’analyse discriminante des modalités d’accouchement au sein d’un échantillon obstétrical. Dans un premier temps, nous construisons des maillages de bassins et de crânes de foetus fossiles grâce à une méthode d’interpolation : le krigeage. Les groupes fossiles considérés sont les Australopithèques, les premiers représentants du genre Homo (PRGH) et les représentants du genre Homo au Pléistocène moyen et supérieur (RPMS). Les dimensions des crânes juvéniles sont utilisées pour estimer « à rebours » les dimensions néonatales à l’aide de courbes de croissance humaine et de chimpanzé. Nous réalisons une simulation numérique de l’accouchement à partir des maillages de ces dyades « virtuelles ». Puis nous réalisons des analyses discriminantes avec un jeu de données issu de mesures réalisées sur le pelviscanner de femmes et sur les mesures du crâne de leur nouveau-né afin de séparer les modalités d’accouchement grâce aux variables foeto-pelviennes. Ces mêmes variables foeto-pelviennes sont mesurées chez les dyades fossiles afin d’identifier, par les analyses discriminantes, leurs modalités d’accouchement les plus probables. Nos résultats suggèrent un accouchement eutocique sans rotation intra-pelvienne chez les Australopithèques, eutocique avec rotation intrapelvienne chez les PRGH, dystocique ou eutocique chez les RPMS, l’accouchement eutocique est caractérisé par une rotation et une incurvation de la trajectoire de descente.The purpose of this thesis is to estimate delivery outcomes for extinct hominids. We therefore use two complementary methods : numerical simulation of childbirth and discriminant analysis of delivery outcomes from an obstetrical sample. First, we use kriging to construct meshes of pelves and neonatal skulls. Fossil hominid specimens included in the study are Australopithecines, early Homo (EH) and middle to early Pleistocene Homo (MEPH). We estimate fetal cranial dimensions with chimpanzee or human cranial growth curve that we reversly use and apply on juveniles skull measurements. “Virtual” dyads are formed from pelves and neonatal skulls. Then, we simulate childbirth of these « virtual » dyads. Different levels of laxity of the sacro-iliac junction and different positions of the fetal head are considered. Finally, we use an obstetrical sample: delivery outcome is noted, CT-scans are used to obtain maternal pelvic measurements and diameters of the fetal head were also measured after delivery. A discriminant analysis is performed using this obstetrical sample to separate delivery outcomes thanks to fetal-pelvic measurements. Fossil dyads were subsequently added in the discriminant analysis to assess delivery outcomes to which they belong. Results suggest small fetal-pelvic constraint for Austalopithecines. This constraint is moderate for EH. Fetal-pelvic constraint is more important for MEPH. We suggest that rotational birth appears with EH. The curved trajectory of the fetal head appears with MEPH. Emergence of rotational birth and curved trajectory of fetal head are probably explained by two major increases in brain size during late and middle Pleistocene

Interval Versus External Pelvimetry: A Validation Study With Clinical Implications

INTRODUCTION: Investigating the correlations between external pelvimetry variables and actual birth canal dimensions has important implications for clinical practice, especially for predicting dystocia. This validation study tests external and internal pelvimetry correlations. METHODS: This single-centered retrospective study included 142 women with records of computed tomography pelvimetry. The correlations between four internal variables (obstetric conjugate, transverse diameters of inlet, midplane, and outlet) and five external variables (intertrochanteric, inter anterosuperior iliac spines, external conjugate, transverse diagonal, and prepubic) were first studied individually. Then, the correlations between each internal variable and the seven external variables were jointly evaluated after adjusting for body mass index. RESULTS: As expected, the external conjugate correlated with the obstetric conjugate ( r = .65; p < .01) but only weakly with the transverse outlet ( r = .21; p < .05). In the simple correlation analysis, the intertrochanteric measure is also correlated with the transverse inlet (TRi), midplane (TRm), and outlet (TRo; r = .542–.672). The transverse diagonal measure marginally correlated with the TRi ( r = .29; p < .01). In the multiple regression models, the intertrochanteric measure is associated with the TRi, TRm, and TRo, while the transverse diagonal is associated with the TRi ( B = .27; p = .01). The prepubic diameter was not a predictor of birth canal dimensions in either simple or multiple regression models. CONCLUSION: Our study confirms that the reduction of the birth canal in some dimensions (i.e., obstetric conjugate and transverse diameters) is predictable with external, accessible pelvic diameters (e.g., external conjugate, transverse diagonal, and intertrochanteric)

: Did our ancestors experience difficulties in childbirth? Estimation of the risk of foetal-pelvic disproportion in modern human and fossil hominins

Version en ligne; pagination non connueThe aim of this study was to assess the risk of foetal-pelvic disproportion in extinct hominins through a comparison of current obstetrical data with fossil data. For the modern sample, we collected pelvic diameters, foetal cranial diameters and delivery outcomes from 92 obstetrical cases (spontaneous vaginal, N = 43; c-section for foetal-pelvic disproportion, N = 34; operative vaginal, N = 15). For the fossil sample, the diameters of 12 pelvises and 6 juvenile skulls were gathered from the literature. Our estimations of neonatal skull sizes were based on (1) juvenile skull measurements and cranial growth curves and (2) the neonatal brain size estimations of DeSilva and Lesnik (2008). A linear discriminant analysis (LDA) was performed on the obstetrical cases. Despite a 35% misclassification error, the results showed a vaginal delivery range, an obstructed delivery range and an intermediate range where delivery outcomes were unpredictable. The multiple combinations between pelvic reconstructions and neonatal cranial estimations were projected onto the LDA and were mostly within the range of normal labour, with probabilities being within the range of normal labour (eutocia) at 0.99 ± 0.01 for Australopithecines; 0.76 ± 0.15 for Homo erectus s.l.; and 0.86 ± 0.08 for Neandertals.Le but de ce travail est d'évaluer le risque de disproportion foetopelvienne au sein d'espèces d'homininés fossiles. L'observation de 92 cas d'accouchements actuels a permis de recueillir les dimensions du bassin maternel, du crâne foetal et l'issue du travail (physiologique : n = 43, césarienne pour " disproportion foetopelvienne " : n = 34 ou extraction instrumentale : n = 15). Les données fossiles proviennent d'une recherche bibliographique incluant 12 reconstructions de bassin et six crânes juvéniles. Les dimensions néonatales fossiles ont été estimées par deux approches : 1) à partir des dimensions des crânes juvéniles et de courbes de croissance humaine et de chimpanzé ; 2) en utilisant les capacités crâniennes néonatales estimées par DeSilva et Lesnik (2008). Malgré un taux d'erreur apparente de 35 %, une analyse discriminante linéaire (ADL) permet de reconnaître une zone d'accouchement eutocique, une zone d'accouchement dystocique et une zone intermédiaire où les variables maternofoetales ne permettent pas de déterminer l'issue du travail. Les combinatoires des couples " virtuels " fossiles entre les reconstructions de bassin et les estimations crâniennes foetales ont été projetées a posteriori sur l'ADL et traduisent le plus souvent un accouchement eutocique. En effet, la probabilité d'appartenance au groupe d'accouchement eutocique des Australopithèques est en moyenne de 0,99 ± 0,01, de 0,76 ± 0,15 pour les Homo erectus s.l. et de 0,86 ± 0,08 pour les Néandertaliens

L'accouchement de nos ancêtres était-il dystocique ? Estimation du risque de disproportion foeto-pelvienne chez l'homme actuel et les hominidés fossiles

Communications orales et affichées de la 1836ème Journée de la Société d'Anthropologie de Paris parues dans Bulletins et Mémoires de la Société d'Anthropologie de Paris , 23 S1-S4

Pelvic and neonatal size correlations in light of evolutionary hypotheses

International audienc

Etude du canal d'accouchement des hominidés fossiles. Apport de la déformation par krigeage d'un basin actuel

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Un cas d’accouchement en occipito-pubien chez Pan troglodytes

L’accouchement de l’Homme moderne est supposé différer de celui des autres primates par plusieurs aspects. Chez notre espèce, l’expulsion du crâne fœtal en présentation céphalique est majoritairement en variété occipito-pubienne et la parturiente est préférentiellement assistée par une tierce personne. Ces spécificités de l’accouchement humain ont été étudiées sous une perspective évolutive et leurs émergences semblent liées à l’accroissement du volume du cerveau et l’acquisition de la bipédie. Dans ce travail, nous analysons un film d’accouchement chez une femelle Pan troglodytes de la Réserve africaine de Sigean (France). Nous vérifions si les spécificités obstétricales humaines précédemment décrites ne sont pas retrouvées dans ce cas. Nous remarquons que le dégagement de la présentation est en occipito-pubien, avec une « auto-assistance » maternelle de la déflexion du crâne au grand couronnement. Il n’y a pas de mouvement de restitution, ni de déchirure périnéale. Ce cas d’accouchement avec une présentation occipito-pubienne s’ajoute aux trois cas décrits en détail dans la littérature et nous amène à reconsidérer les hypothèses évolutives liées à l’obstétrique. Néanmoins, le nombre de films d’accouchement chez Pan troglodytes reste insuffisant pour décrire la diversité des variétés d’expulsion.The birthing process in modern humans is supposed to be different from non-human primate birth. In humans the foetal head exits the birth canal mostly in occiput anterior position and the pregnant woman frequently seeks assistance. These characteristics have been interpreted from an evolutionary perspective and they are supposed to be due to the physical constraints related to the increase in brain size and bipedal locomotion. In this study, we analyse a close-up video recording of the delivery of a female Pan troglodytes from the Réserve africaine de Sigean (France). Our aim is to check whether the human birth characteristics are absent in this case. We observe a human-like occiput anterior position at the expulsion with a manual deflexion of the foetal head performed by the mother herself. There are neither restitution movements nor perineal tears. Our observation, together with the three others cases of occiput anterior positions described in the literature, leads us to question the evolutionary hypotheses related to human birth. However, more videos of Pan troglodytes birth are needed to investigate the diversity of the foetal head position during expulsion