Doctoral Dissertation Improvement: Bipedal Obstetric Load and the Evolution of Human Lumbopelvic Sexual Dimorphism

发育中的胎儿会改变母亲的身体比例和质量分布，导致脊柱和骨盆不稳定。这项研究假设，人类腰椎和骨盆解剖的性别二型性在一定程度上代表了女性对与胎儿负荷的生物力学相关的结构性风险的独特适应。这一假设不同于流行的观点，即腰盆性二型性完全与分娩选择有关，分娩选择有利于母亲的产道足够宽敞，可以分娩大脑大或身体大的新生儿。作为解释人类腰盆性二态范围的框架，目前的结论可能会受到限制，因为只关注与分娩事件直接相关的骨盆形态，而没有考虑随之而来的生殖负荷的压力。腰椎和腰椎性二型性一直被解释为与骨盆相顺应，这掩盖了椎骨在躯干生物力学中发挥更直接功能的可能性。虽然怀孕是间歇性的，但胎儿负荷的持续时间和复发对姿势和运动骨骼施加了显著的压力，不仅对现代人，而且对早期的两足动物也有影响。对70名女性和70名男性，以及13种非人类灵长类动物(包括习惯性直立的类群)的600个个体进行形态计量学研究，以检验人类腰盆骨骼的性别二态比其他灵长类更大的预测。为了研究胎儿负荷对腰盆骨骼的生物力学影响，对20名孕妇的脊柱负荷模式进行了运动学分析，包括母体重心位置、下背部曲线和骨盆前倾角。实验方法将测试关于怀孕期间人类女性脊柱和骨盆的体重重新分配和负载的假设；而比较形态计量学方法将把这些结果放在更广泛的系统发育和进化背景下。这个项目的广泛影响有三个方面。首先，重建两足产科负荷的适应模式将为目前由临床实践定义的人类体验提供进化深度。其次，这项研究将为将在项目管理方面获得学术和实践培训的本科生助理提供实践研究经验。第三，由于志愿者参与了这项研究，女性公众和学术界之间的互动将有助于促进女性获得当前研究的机会，并最终将为女性的生命教育提供信息。

A developing fetus modifies maternal body proportions and mass distribution introducing instability to the vertebral column and pelvis. This study hypothesizes that human sexual dimorphism of lumbar vertebral and pelvic anatomy represents, in part, unique female adaptations to structural risks associated with biomechanics of fetal load. The hypothesis differs from the prevailing view that lumbopelvic sexual dimorphism is entirely related to parturitional selection favoring a maternal birth canal spacious enough for delivery of a large-brained or large bodied neonate. As a framework for interpreting the scope of human lumbopelvic sexual dimorphism, current conclusions may be limited by focusing only on pelvic morphology directly related to the birthing event and by failure to consider the attendant stresses of reproductive load. Persistent interpretation of sexual dimorphism in lumbar and sacral vertebrae as compliant to the pelvis obscures the possibility that the vertebrae perform a more immediate function in trunk biomechanics. Although pregnancy is intermittent, the duration and recurrence of fetal load exert marked stress on the postural and locomotor skeleton, holding implications not only for modern humans but for earlier bipeds as well. Sexual dimorphism of the lumbopelvic skeleton will be examined morphometrically in 70 human females and 70 human males and in a comparative sample of 600 individuals of 13 species of nonhuman primates, including habitually erect taxa, to examine the prediction that lumbopelvic sexual dimorphism is greater in humans than in other primates. To investigate the biomechanical impact of human fetal load on the lumbopelvic skeleton, spinal loading patterns of twenty pregnant females will be kinematically identified for position of the maternal center of mass, curve of the lower back and angle of anterior pelvic tilt. The experimental approach will test hypotheses on weight redistribution and loading of the human female spine and pelvis during pregnancy; while the comparative morphometric approach will place these results into broader phylogenetic and evolutionary contexts. The wider effects of this project are threefold. First, reconstruction of adaptive patterns in bipedal obstetric load will provide evolutionary depth to a human experience currently defined by clinical practice. Second, the study will provide hands-on research experience for undergraduate assistants who will gain both academic and practical training in project management. Third, as a result of volunteer participation in this study, interactions between the female public and the academic community will help to advance women's access to current research and will ultimately inform the life education of women.