Expanding the evolutionary explanations for sex differences in the human skeleton

While the anatomy and physiology of human reproduction differ between the sexes, the effects of hormones on skeletal growth do not. Human bone growth depends on estrogen. Greater estrogen produced by ovaries causes bones in female bodies to fuse before males\u27 resulting in sex differences in adult height and mass. Female pelves expand more than males\u27 due to estrogen and relaxin produced and employed by the tissues of the pelvic region and potentially also due to greater internal space occupied by female gonads and genitals. Evolutionary explanations for skeletal sex differences (aka sexual dimorphism) that focus too narrowly on big competitive men and broad birthing women must account for the adaptive biology of skeletal growth and its dependence on the developmental physiology of reproduction. In this case, dichotomizing evolution into proximate‐ultimate categories may be impeding the progress of human evolutionary science, as well as enabling the popular misunderstanding and abuse of it

Baby steps towards linking calcaneal trabecular bone ontogeny and the development of bipedal human gait.

Trabecular bone structure in adulthood is a product of a process of modelling during ontogeny and remodelling throughout life. Insight into ontogeny is essential to understand the functional significance of trabecular bone structural variation observed in adults. The complex shape and loading of the human calcaneus provides a natural experiment to test the relationship between trabecular morphology and locomotor development. We investigated the relationship between calcaneal trabecular bone structure and predicted changes in loading related to development of gait and body size in growing children. We sampled three main trabecular regions of the calcanei using micro-computed tomography scans of 35 individuals aged between neonate to adult from the Norris Farms #36 site (1300 AD, USA) and from Cambridge (1200-1500 AD, UK). Trabecular properties were calculated in volumes of interest placed beneath the calcaneocuboid joint, plantar ligaments, and posterior talar facet. At birth, thin trabecular struts are arranged in a dense and relatively isotropic structure. Bone volume fraction strongly decreases in the first year of life, whereas anisotropy and mean trabecular thickness increase. Dorsal compressive trabecular bands appear around the onset of bipedal walking, although plantar tensile bands develop prior to predicted propulsive toe-off. Bone volume fraction and anisotropy increase until the age of 8, when gait has largely matured. Connectivity density gradually reduces, whereas trabeculae gradually thicken from birth until adulthood. This study demonstrates that three different regions of the calcaneus develop into distinct adult morphologies through varying developmental trajectories. These results are similar to previous reports of ontogeny in human long bones and are suggestive of a relationship between the mechanical environment and trabecular bone architecture in the human calcaneus during growth. However, controlled experiments combined with more detailed biomechanical models of gait maturation are necessary to establish skeletal markers linking growth to loading. This has the potential to be a novel source of information for understanding loading levels, activity patterns, and perhaps life history in the fossil record.the Arts and Humanities Research Council Doctoral Training Programme, 1503975 European Research Council under the European Union's Seventh Framework Programme (FP/ 2007e2013)/ERC Grant Agreement n.617627 National Science Foundation Grant BCS-061709

Sudden Infant Death Syndrome

Evolutionary understanding of infant biology emphasises that human newborns have unique needs due to poorly developed neuromuscular capabilities, and physiological vulnerability in the absence of a caregiver. This perspective has been used to critically analyse Western infant care, propose testable hypotheses regarding sudden infant death syndrome (SIDS) and infant sleep and create interventions for policy and practice. This chapter provides an overview of conventional SIDS research and research informed by consideration of infants' evolutionary needs and expectations. Focusing primarily on infant sleep location, we illustrate how this research has been translated into policy and practice around the world