The obstetric pelvis of A.L. 288-1 (Lucy (original) (raw)
Related papers
Primate pelvic anatomy and implications for birth
Philosophical transactions of the Royal Society of London. Series B, Biological sciences, 2015
The pelvis performs two major functions for terrestrial mammals. It provides somewhat rigid support for muscles engaged in locomotion and, for females, it serves as the birth canal. The result for many species, and especially for encephalized primates, is an 'obstetric dilemma' whereby the neonate often has to negotiate a tight squeeze in order to be born. On top of what was probably a baseline of challenging birth, locomotor changes in the evolution of bipedalism in the human lineage resulted in an even more complex birth process. Negotiation of the bipedal pelvis requires a series of rotations, the end of which has the infant emerging from the birth canal facing the opposite direction from the mother. This pattern, strikingly different from what is typically seen in monkeys and apes, places a premium on having assistance at delivery. Recently reported observations of births in monkeys and apes are used to compare the process in human and non-human primates, highlighting si...
The Anatomical Record, 2017
No bone in the human postcranial skeleton differs more dramatically from its match in an ape skeleton than the pelvis. Humans have evolved a specialized pelvis, well-adapted for the rigors of bipedal locomotion. Precisely how this happened has been the subject of great interest and contention in the paleoanthropological literature. In part, this is because of the fragility of the pelvis and its resulting rarity in the human fossil record. However, new discoveries from Miocene hominoids and Plio-Pleistocene hominins have reenergized debates about human pelvic evolution and shed new light on the competing roles of bipedal locomotion and obstetrics in shaping pelvic anatomy. In this issue, 13 papers address the evolution of the human pelvis. Here, we summarize these new contributions to our understanding of pelvic evolution, and share our own thoughts on the progress the field has made, and the questions that still remain.
The female pelvis and its significance in human evolution
When I discovered a connection between the four evolutionary temperaments (hunter-gatherers, farmers and pastoralists) and some anatomical features, like facial structure and body shape, the pelvis was one of the first anatomical structures I checked out. The female pelvis has two crucial functions: 1. Locomotion (survival, subsistence) 2. Childbirth (reproduction) If there are structural differences in female pelvises, the obvious thing is to assume that those are adaptations to differences in locomotion for different subsistence strategies (hunters, gatherers, farmers and pastoralists). However, different reproductive strategies may also be at play as farmers and herders have much higher reproductive rates than hunter-gatherers (every 2 years vs every 4 years). To my great joy, I really did find four differently shaped types of the pelvis: • The gynaecoid pelvis is the so-called normal female pelvis. Its inlet is either slightly oval, with a greater transverse diameter, or round. The interior walls are straight, the subpubic arch wide, the sacrum shows an average to backward inclination, and the greater sciatic notch is well rounded. Because this type is spacious and well proportioned there is little or no difficulty in the birth process. Caldwell and his co-workers found gynaecoid pelves in about 50 per cent of specimens. • The platypelloid pelvis has a transversally wide, flattened shape, is wide anteriorly, greater sciatic notches of male type, and has a short sacrum that curves inwards reducing the diameters of the lower pelvis. This is similar to the rachitic pelvis where the softened bones widen laterally because of the weight from the upper body resulting in a reduced anteroposterior diameter. Giving birth with this type of pelvis is associated with problems, such as transverse arrest. Less than 3 per cent of women have this pelvis type. • The android pelvis is a female pelvis with masculine features, including a wedge or heart shaped inlet caused by a prominent sacrum and a triangular anterior segment. The reduced pelvis outlet often causes problems during childbirth. In 1939 Caldwell found this type in one third of white women and in one sixth of non-white women. • The anthropoid pelvis is characterized by an oval shape with a greater anteroposterior diameter. It has straight walls, a small subpubic arch, and large sacrosciatic notches. The sciatic spines are placed widely apart and the sacrum is usually straight resulting in deep non-obstructed pelvis. Caldwell found this type in one quarter of white women and almost half of non-white women. (from Wikipedia) My joy became more moderate when I tried to match the four pelvis shapes to the four temperaments. The percentages simply did not line up. Farmer types make up about 50% and so does the distribution of the gynaecoid pelvis. However, the percentage of the other types didn’t work out. So, I gave up my attempt to match them. That is until recently an online friend (thanks Jari) contacted me telling me about this pattern. I told him that the percentage didn’t align and he encouraged me to continue my research, as a perfect match wouldn’t be necessary. A tentative match produces the following pictures: The gynaecoid type matches with farmer types not only in percentages but also regarding the fact that this is the shape that produces the least complications during childbirth, i.e. it is adapted to high fertility rates. Even though pastoralist types may be more r-selected, farmer types probably had the higher birth rates due to sedentism throughout history. On the flip side, female hunter types would have had the lowest fertility rates, slightly lower than the caregiving gatherer types as they would have had less time for nursing, having an evolutionary providing profile. The fertility rates in foragers are furthermore limited by later menarche as well as earlier menopause. Menarche in different forager groups The platypelloid type is the one that has the most complications for childbirth. My wife has a hunter-type friend who had huge difficulties giving birth to all of her four children (all cesarean section). Unfortunately, I haven’t been able to find data from forager societies, however, the following piece of research gives us some clues: In our earliest upright ancestors, fundamental alterations of the pelvis compared with non-human primates facilitated bipedal walking. Further changes early in hominin evolution produced a platypelloid birth canal in a pelvis that was wide overall, with flaring ilia. This pelvic form was maintained over 3–4 Myr with only moderate changes in response to greater habitat diversity, changes in locomotor behaviour and increases in brain size. It was not until Homo sapiens evolved in Africa and the Middle East 200 000 years ago that the narrow anatomically modern pelvis with a more circular birth canal emerged. (source) This means the platypelloid type is evolutionarily the oldest type of pelvis and can therefore be attributed to hunter-gatherer types. A more circular shape evolved in gatherer women around the time of the emergence of modern Homo Sapiens. Empirical research could easily show if the remaining two types of pelvis are correlated with farmer and herder types. The four types of pelvis should also be somewhat correlated with body shape and body fat distribution, which may be very different in hunter-gatherers, farmers and herders. Future research may uncover some more interesting connections. This post is dedicated to Jari for encouraging my research
Anatomy, Development, and Function of the Human Pelvis
Anatomical record (Hoboken, N.J. : 2007), 2017
The pelvis is an anatomically complex and functionally informative bone that contributes directly to both human locomotion and obstetrics. Because of the pelvis' important role in obstetrics, it is one of the most sexually dimorphic bony elements of the human body. The complex intersection of pelvic dimorphism, locomotion, and obstetrics has been reenergized by exciting new research, and many papers in this special issue of the pelvis help provide clarity on the relationship between pelvic form (especially female) and locomotor function. Compared to the pelvis of our ape relatives, the human pelvis is uniquely shaped; it is superoinferiorly short and stout, and mediolaterally wide-critical adaptations for bipedalism that are already present in some form very early in the history of the hominin lineage. In this issue, 13 original research papers address the anatomy, development, variation, and function of the modern human pelvis, with implications for understanding the selection ...
Locomotor function and the evolution of the primate pelvis
The bony pelvis is a pivotal component of the locomotor system, as it links the hindlimb with the trunk and serves as anchorage for the primary propulsive musculature. Its shape is therefore expected to be adapted to the biomechanical demands of habitual locomotor behavior. However, because the relationship between locomotor mechanics and pelvic morphology is not well understood, the adaptive significance of particular pelvic traits and overall pelvic shape remains unclear.
Sexual dimorphism in the human pelvis: Testing a new hypothesis
HOMO, 2005
Sexual dimorphism in the human pelvis is inferentially related to parturition. Investigators disagree about the identification and obstetric significance of pelvic dimorphism. Benefiting from a large sample of complete skeletons from the Coimbra Identified Skeletal Collection, we show that the dimensions of the true pelvis (birth canal) that are most sexually dimorphic (that is, the dimensions of females are greater than males) are those which are related to biparietal deformation, which often leads to the death of the human neonate. These dimensions are: the anteroposterior diameter of the inlet (index of dimorphism ¼ 108.41), the transverse diameter of the bispinous midplane (index of dimorphism ¼ 117.13) and the transverse diameter of the outlet (index of dimorphism ¼ 112.3). Therefore, sexual dimorphism in the human pelvis is a reflection of differential selection on the two sexes. These results may stimulate further studies with a fresh approach regarding the fossil and comparative evidence for when and how the modern pattern of birth has evolved.
The fossil record of the human pelvis reveals the selective priorities acting on hominin anatomy at different points in our evolutionary history, during which mechanical requirements for locomotion, childbirth and thermo-regulation often conflicted. In our earliest upright ancestors, fundamental alterations of the pelvis compared with non-human primates facilitated bipedal walking. Further changes early in hominin evolution produced a platypelloid birth canal in a pelvis that was wide overall, with flaring ilia. This pelvic form was maintained over 3–4 Myr with only moderate changes in response to greater habitat diversity, changes in locomotor behaviour and increases in brain size. It was not until Homo sapiens evolved in Africa and the Middle East 200 000 years ago that the narrow anatomically modern pelvis with a more circular birth canal emerged. This major change appears to reflect selective pressures for further increases in neonatal brain size and for a narrow body shape associated with heat dissipation in warm environments. The advent of the modern birth canal, the shape and alignment of which require fetal rotation during birth, allowed the earliest members of our species to deal obstetrically with increases in encephalization while maintaining a narrow body to meet thermoregulatory demands and enhance locomotor performance.
Developmental evidence for obstetric adaptation of the human female pelvis
Proceedings of the National Academy of Sciences of the United States of America, 2016
The bony pelvis of adult humans exhibits marked sexual dimorphism, which is traditionally interpreted in the framework of the "obstetrical dilemma" hypothesis: Giving birth to large-brained/large-bodied babies requires a wide pelvis, whereas efficient bipedal locomotion requires a narrow pelvis. This hypothesis has been challenged recently on biomechanical, metabolic, and biocultural grounds, so that it remains unclear which factors are responsible for sex-specific differences in adult pelvic morphology. Here we address this issue from a developmental perspective. We use methods of biomedical imaging and geometric morphometrics to analyze changes in pelvic morphology from late fetal stages to adulthood in a known-age/known-sex forensic/clinical sample. Results show that, until puberty, female and male pelves exhibit only moderate sexual dimorphism and follow largely similar developmental trajectories. With the onset of puberty, however, the female trajectory diverges subst...
Allometric scaling and locomotor function in the primate pelvis
Identification of positional behavior adaptation in the pelvis of primates is complicated by possible confounding effects of body size and phylogeny. Previous work on primate pelvic allometry has focused primarily on sexual dimorphism and its relationship to obstetric constraints in species with large fetal size relative to maternal size. This study investigates patterns of pelvic scaling with a specific aim to understand how pelvic scaling relates to locomotor function. Patterns of scaling of nine pelvic dimensions were examined in a broad comparative sample of 40 species of primates, covering both haplorhines and strepsirrhines, while accounting for phylogenetic nonindependence. Phylogenetic reduced major axis regressions on pelvic scaling patterns suggest that primate-wide patterns are reflected in haplorhine-and strepsirrhine-specific analyses. Many measures scale isometrically with pelvis size, but notably, features of the ilium tend to scale allometrically. As predicted, ilium width and lower ilium crosssectional area scale with positive allometry, while lower iliac height scales with negative allometry. Further regression analyses by locomotor group suggest that these ilium measures, as well as pubic symphysis and ischium lengths, differ in their scaling patterns according to locomotor mode. These results suggest that scaling differences within primates, when present, are related to functional differences in locomotor behavior and mechanics. This study supports recent work that identifies adaptations to locomotor loading in the ilium and highlights the need for a better understanding of the relationship between pelvic structural mechanics and the mechanical requirements of primate locomotion. Am J Phys Anthropol 000:000-000, 2015.