Comparative primate birth mechanics and the evolution of human childbirth

Modern humans have large, encephalized neonates, delivered through an anteroposteriorly narrow maternal pelvis constrained by adaptation to bipedality. As a result, human birth is unusually laborious, difficult, and dangerous. The evolutionary background for these difficulties is unclear. Previous comparative studies of nonhuman primates have focused on the pelvic inlet, which is a region of constraint in humans but not in other primates. Therefore, the true obstetric constraints in other species remain unknown. This dissertation documents and quantifies human and other primate birth-canal morphology between the three traditional obstetric planes (inlet, midplane, and outlet). Computer-generated images of scanned specimens of 23 extant anthropoid species and five fossil hominins are used to compare the entire birth canals as three-dimensional entities, documenting and analyzing the functionally relevant metrics of the maternal pelvis and the fetus and their species-specific obstetric constraints. In fossil hominin species for which pelvic material is fragmentary, composite pelves were reconstructed. Measurements on these pelves allow for an estimation of the factors (fetal head and shoulders, pelvic morphology) that produce points of potential dystocia, and shed light on how the modern human birth mechanism evolved. The results of these analyses indicate that some non-human primates have obstetric constraints that exceed those of modern humans. The cephalopelvic disproportion in these species is alleviated through various mechanisms which are unattainable in humans, such as a face-first fetal presentation. Human childbirth can no longer be described as uniquely difficult compared to that of the other primates. Among fossil hominins, birth canal morphology exhibits shape variations that differ from those in modern humans and would have promoted different patterns and mechanisms of birth. The locations of maximum obstetric constraints also vary among hominin species, and the pattern of interspecific variation does not present a linear evolutionary trajectory from “easy” to “difficult” childbirth. The risk of prolapse that accompanies hominin bipedality does result in an adaptation to reduce obstetric constraints, fetal cranial molding, which may have arisen in the hominin lineage ~700,000 years earlier than previously thought

Automated brain masking of fetal functional MRI with open data

Fetal resting-state functional magnetic resonance imaging (rs-fMRI) has emerged as a critical new approach for characterizing brain development before birth. Despite the rapid and widespread growth of this approach, at present, we lack neuroimaging processing pipelines suited to address the unique challenges inherent in this data type. Here, we solve the most challenging processing step, rapid and accurate isolation of the fetal brain from surrounding tissue across thousands of non-stationary 3D brain volumes. Leveraging our library of 1,241 manually traced fetal fMRI images from 207 fetuses, we trained a Convolutional Neural Network (CNN) that achieved excellent performance across two held-out test sets from separate scanners and populations. Furthermore, we unite the auto-masking model with additional fMRI preprocessing steps from existing software and provide insight into our adaptation of each step. This work represents an initial advancement towards a fully comprehensive, open-source workflow, with openly shared code and data, for fetal functional MRI data preprocessing

The developing juvenile talus:Radiographic identification of distinct ontogenetic phases and structural trajectories

Trabecular bone architecture in the developing skeleton is a widely researched area of bone biomechanics; however, despite its significance in weight-bearing locomotion, the developing talus has received limited examination. This study investigates the talus with the purpose of identifying ontogenetic phases and developmental patterns that contribute to the growing understanding of the developing juvenile skeleton. Colour gradient mapping and radiographic absorptiometry were utilised to investigate 62 human tali from 38 individuals, ranging in age-at-death from 28 weeks intrauterine to 20 years of age. The perinatal talus exhibited a rudimentary pattern comparable to the structural organisation observed within the late adolescent talus. This early internal organisation is hypothesised to be related to the vascular pattern of the talus. After 2 years of age, the talus demonstrated refinement, where radiographic trajectories progressively developed into patterns consistent with adult trabecular organisation, which are linked to the forces associated with the bipedal gait, suggesting a strong influence of biomechanical forces on the development of the talus.</p

Computer modelling of the development of the trabecular architecture in the human pelvis

The influence of mechanical loading upon bone growth and remodelling has been widely studied. It has been suggested that functional bone growth is evident within the human adult pelvis, where the internal trabecular structure is purported to align to the principal strain trajectories induced during bipedal locomotion. Ontogenetic studies of the juvenile pelvis have observed that trabecular bone growth becomes progressively ordered from&nbsp; an initial randomised patterning. This has lead to theories linking the gradual structural optimisation of&nbsp; trabecular bone to the mechanical forces associated with the development of juvenile locomotion. However, recent studies have observed partially optimised trabecular structures within the human fetal and neonatal&nbsp; pelvis, in contrast to previous observations. The possible genetic and mechanical factors which cause the in utero formation of these trabecular structures, which are usually associated with a weight bearing function,&nbsp; remains unknown. Therefore, this thesis aimed to investigate the influence of the mechanical strains associated with juvenile movements, upon the growth of pelvic trabecular bone.Biomechanical analyses were performed on digitised models of juvenile pelvic specimens belonging to the&nbsp; Scheuer collection. Digitised models of a prenatal, 1 year, 8 year and 19 year old pelvis were constructed&nbsp; through processing mircocomputed tomography scan data. A geometric morphometric reconstruction technique was devised which enabled the creation of hemi-pelvic models from originally disarticulated bone specimens. This reconstruction technique was validated through a close morphological comparison between a&nbsp; reconstructed hemi-pelvis, and its originally articulated CT data. The muscular and joint forces associated with&nbsp; in utero movements and bipedal locomotion, were computed through musculoskeletal simulations. A prenatal&nbsp; musculoskeletal model was constructed to replicate the in utero mechanical environment, and simulated&nbsp; interactions between the fetal leg and the womb wall. The forces associated with bipedal locomotion were&nbsp; evaluated through analysis of a pre-defined subject-specific musculoskeletal model. An attempt was made to&nbsp; validate the modelling technique of altering generic musculoskeletal models to create subject-specific&nbsp; representations. However, comparisons between computed and experimentally recorded muscle activities&nbsp; proved inclusive, although this was attributed to uncertainties in the accuracy of the experimental data. A series of finite element analyses computed the strain distributions associated with the predicted musculoskeletal&nbsp; loading. A range of load regimes were applied to each juvenile pelves, and were based upon the computed&nbsp; musculoskeletal forces and the maximum isometric force capabilities of the pelvic muscles. However, despite&nbsp; the differences between the applied load regimes, the predicted von Mises and compressive strain distributions&nbsp; displayed similarities for all the ages analysed. All the predicted distributions were characterised&nbsp; by high strains within the inferior ilium, which correlated to a region of high trabecular organisation. The high&nbsp; strain magnitudes then travelled superiorly in either a gradual or rapid dissipation, both of which did not&nbsp; produce a distribution which correlated to the pelvic trabecular histomorphometry. Therefore, no strain&nbsp; distribution was predicted with divergence of the inferior strains to the anterior and posterior regions of the ilium,&nbsp; as observed with the trabecular trajectories within the pelvis.As the predicted von Mises and compressive strain distributions failed to match the complete iliac trabecular&nbsp; histomorphometry, it was suggested that the in utero formation of partially optimised trabecular growth is&nbsp; possibly due to generic factors. This thesis provided initial investigations into the musculoskeletal and&nbsp; mechanical loading of the juvenile pelvis, although future work is required to develop the applied modelling&nbsp; techniques to fully determine the influence of the mechanical strains

Secular Change of the Modern Human Bony Pelvis: Examining Morphology in the United States using Metrics and Geometric Morphometry

The human bony pelvis has evolved into its current form through competing selective forces. Bipedalism and parturition of large headed babies resulted in a form that is a complex compromise. While the morphology of the human pelvis has been extensively studied, the changes that have occurred since the adoption of the modern form, the secular changes that continue to alter the size and shape of the pelvis, have not received nearly as much attention. This research aims to examine the changes that have altered the morphology of the human bony pelvic girdle of individuals in the United States born between 1840 and1981. Secular changes in the human skeleton have been documented. Improvements in nutrition, decreased disease load, exogamy, activity, climate, and other factors have led to unprecedented growth in stature and weight. The size and shape of the pelvic canal, os coxa, and bi-iliac breadth were all examined in this study. Coordinate data from males and females, blacks and whites were digitized. Calculated inter-landmark data was analyzed using traditional metric methods and the coordinate data was analyzed using 3D geometric morphometrics. After separating the samples into cohorts by sex and ancestry, results indicate that there is secular change occurring in the modern human bony pelvis. Changes in shape are significant across the groups while only white males exhibit increases in size. The dimensions of the pelvic canal have changed over time. The birth canal is becoming more rounded with the inlet anteroposterior diameter and the outlet transverse diameter becoming longer. These diameters, once limiters, are believed to have led to an adoption of the rotational birth method practiced by modern humans. In addition, the bowl of the pelvis is becoming less flared. Childhood improvements in nutrition and decreases in strenuous activity may be the cause of the dimension changes in the bony pelvis. The similar changes across both sexes and ancestries indicate a similar environmental cause. However, it is likely a combination of factors that are difficult to tease apart. Whether the increases continue remains to be determined

Plasticity and Population Structure: Exploring Secular Trends in the Three- Dimensional Cranial Morphology of the Modern Portuguese

Significant secular changes have been documented in several worldwide populations over the past 200 years; these changes include increased stature and weight, increased cranial vault height, and a narrowing of the cranial vault width (Angel 1976; Boas 1912; Jantz 2001; Jonke et al. 2007; Little et al. 2006). A variety of hypotheses have been proposed as to the origins of the observed changes. This dissertation uses a documented collection of skeletons from the 19th and 20th centuries to describe the precise nature of the changes using three-dimensional methods and explores possible causes underlying the changes including individual environmental effects, demographic parameters, and spatial effects. Three-dimensional cranial landmarks from 500 identified individuals from the New Lisbon Skeletal collection in Lisbon, Portugal were collected along with available demographic data. The birth years represented in the sample range from 1805-1960. The Portuguese sample provides the opportunity for understanding the genetic and environmental components of the observed changes. The highly circumscribed nature of the skeletal collection, which contains only individuals from the relatively homogenous Portuguese population, enables a comparison of the observed changes with information about individual environmental effects, such as socioeconomic status and health status. The impact of the demographic transition that characterizes modern populations is also examined; the modern demographic transition is characterized by a decrease in mortality followed by a decrease in fertility. Also, information regarding the place of birth and place of death for individuals in the sample is used to model the spatial effects on cranial morphology and to demonstrate the maintenance of genetic structure in spite of significant secular changes. In addition to providing a unique sample for testing theories related to the causes of secular trends, this research also provides a new way of documenting secular trends. In previous research, secular changes have primarily used traditional linear craniometric data, anthropometric data, or conscript records to document change. The use of three-dimensional data enables a more exact description of changes in the cranial form and provides the opportunity for a more precise understanding of the basis for change

Craniofacial growth and development in modern humans and Neanderthals

This thesis assesses craniofacial growth, development and the dynamics of developmental interactions among cranial regions in modern humans and Neanderthals. To these ends, virtual segmentation, landmarking and Geometric Morphometrics (GM) are applied to an ontogenetic series of the whole crania of 68 H. sapiens and 12 H. neanderthalensis. First, the ontogenetic shape and form changes in the cranial vault, base and face are explored, and the locations and magnitudes of these changes are discussed. Secondly, allometric scaling is tested for differences among different age classes in the three regions of the cranium. In addition, the degree of covariation among these and how it changes over time is investigated.The study then focuses on interactions among facial regions. First, similar analyses as those used in the study of the cranium are applied to compare growth, development and covariation among parts of the face in different age classes. Additionally, a sample of 227 modern humans from 0 to 6 years of age is analysed using path analysis, to investigate the cascade of interactions and relative contributions of soft tissue and skeletal elements to the overall growth and development of the face. Last, the facial morphology of H. sapiens is compared to that of H. neanderthalensis and their ontogenetic trajectories are tested for divergence. Novel method registration-free colour maps are used to visualise regional changes during growth and development and to compare the morphologies of the two species. Covariation among facial elements is also compared to assess potential differences in developmental interactions. In modern humans, the results show that allometry and covariation change significantly among age classes and between cranial regions during ontogeny and that covariation is stronger in younger subadults than in older subadults and adults. Among modern humans, significantly divergent trajectories are observed between age classes during ontogeny in all three cranial regions. In the modern human face, allometric scaling also differs among age stages in each region. Interestingly, covariation among facial regions becomes progressively non-significant with time, with the exception of those including the nose and maxilla. Path analysis in modern humans shows a large contribution of the proxy used for nasal septum to the overall facial development. Soft tissues contribute only locally to the development of some skeletal elements of the face. Major aspects of the differences between adult modern humans and Neanderthals are already present in the youngest individuals. However, additional differences arise through differences in the degree of change in facial size and significantly divergent allometric trajectories. Analyses of covariation among Neanderthal facial regions suffer from small sample size but, where significant, suggest that the interactions among cranial components are similar to those in modern humans, with some differences

The avian lingual and laryngeal apparatus within the context of the head and jaw apparatus, with comparisons to the mammalian condition: Functional morphology and biomechanics of evaporative cooling, feeding, drinking, and vocalization

© Springer International Publishing AG 2017. All rights reserved. The lingual and laryngeal apparatus are the mobile and active organs within the oral cavity, which serves as a gateway to the respiratory and alimentary systems in terrestrial vertebrates. Both organs play multiple roles in alimentation and vocalization besides respiration, but their structures and functions differ fundamentally in birds and mammals, just as the skull and jaws differ fundamentally in these two vertebrate classes. Furthermore, the movements of the lingual and laryngeal apparatus are interdependent with each other and with themovements of the jaw apparatus in complex and littleunderstood ways. Therefore, rather than updating the existing numerous reviews of the diversity in lingual morphology of birds, this chapter will concentrate on the functionalmorphological interdependences and interactions of the lingual and laryngeal apparatus with each other and with the skull and jaw apparatus. It Will