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

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

AbstractInternational audienc

Pelvic and neonatal size correlations in light of evolutionary hypotheses

International audienc

Exploratory study of the three-dimensional morphological variation of the jaw associated to teeth loss

Purpose : The aim of this study is to evaluate the morphological variability in mandibles with different types of edentulism, comparing the use of traditional morphometrics and tridimensional geometric morphometrics. Methods : Traditional morphometrics and geometric morphometrics (GM) exploratory analysis, by principal components (PCs) and PC scores, were performed on a sample of 24 cadaveric hemi mandibles. A digital reconstruction of 3D surfaces of each specimen was obtained by CT scans segmentation. The mandibles were divided in three groups: full dentition (G1), partial edentition (G2) and total edentition (G3). The results of the two methods were compared in relation to the morphological variability determined with each method. Results : Both methods were consistent in terms of morphological variability between the defined groups. The main shape variations observed were a decrease in mandibular body height, a widening of the cross sectional morphology on the symphysis, a shorten-narrowed Ramus and a deeper sigmoid notch, in the partially or totally edentition groups, compared to the full dentition group. Discussion : The general patterns of morphological variations associated with edentulism that have been reported in literature could be visualized with GM method, which had not been previously used for this purpose. The GM methods could offer a more detailed definition of shape variations, which is critical in a clinical context. Moreover, GM allowed defining configurations of mean morphologies and an image library with different types of morphological variations

Exploratory study of the three-dimensional morphological variation of the jaw associated to teeth loss

Purpose : The aim of this study is to evaluate the morphological variability in mandibles with different types of edentulism, comparing the use of traditional morphometrics and tridimensional geometric morphometrics. Methods : Traditional morphometrics and geometric morphometrics (GM) exploratory analysis, by principal components (PCs) and PC scores, were performed on a sample of 24 cadaveric hemi mandibles. A digital reconstruction of 3D surfaces of each specimen was obtained by CT scans segmentation. The mandibles were divided in three groups: full dentition (G1), partial edentition (G2) and total edentition (G3). The results of the two methods were compared in relation to the morphological variability determined with each method. Results : Both methods were consistent in terms of morphological variability between the defined groups. The main shape variations observed were a decrease in mandibular body height, a widening of the cross sectional morphology on the symphysis, a shorten-narrowed Ramus and a deeper sigmoid notch, in the partially or totally edentition groups, compared to the full dentition group. Discussion : The general patterns of morphological variations associated with edentulism that have been reported in literature could be visualized with GM method, which had not been previously used for this purpose. The GM methods could offer a more detailed definition of shape variations, which is critical in a clinical context. Moreover, GM allowed defining configurations of mean morphologies and an image library with different types of morphological variations

Investigating the possible role of placenta position in road accident consecutive foetal loss

The main objective of this study is to evaluate the possibility of using a numerical model of a pregnant woman to understand placenta injury mechanisms in car accident situations. As a first step, a finite element (FE) model was developed by adding a gravid uterus in the already available Radioss Humos _R full human body model. This numerical model was evaluated using a cadaver tests approach. Simulated and experimental gravid uterus kinematics were compared and found in good agreement. Indentation tests also were performed on fresh placenta specimens. A placenta FE segment was then implemented into the full pregnant body model at different locations. For a simulated frontal impact at moderate speed, the placenta position was not found to significantly influence the abruption risk. Our results illustrate the potential of numerical simulation to improve the description of injury mechanisms related to pregnant women, in particular the placenta abruption. Further work is, however, required to develop the experimental tests database used for the model validation, and to investigate sensibility to maternal morphology. car crash; numerical model; placenta abruption; foetal death; traum

Evaluation of a new security system to reduce thoracic injuries in case of motorcycle accidents

A study sponsored by National Highway Traffic Safety Administration (NHTSA) in 1981 showed that the most deadly injuries to the accident victims were injuries of the chest and head. In this context, the present paper focuses on the use of the numerical simulation to predict rib fractures in case of motorcycle accidents and to evaluate a new safety system, i.e. an airbag integrated in the jacket. Different simulations were performed, with and without airbag, according to experimental tests (pendulum subsystem tests with post-mortem human subjects (PMHS)) to evaluate the influence of various parameters. For each configuration test, we analysed the load versus time curve of the pendulum and performed an injury report to evaluate ribs fractures. Concerning the airbag system, the study showed that this type of protection increases motocyclist's security. Indeed, for each simulations test, performed with airbag, no injuries were noted when the airbag was used. Finite element model; human; motorcycle; trauma; safety; cras