Doctoral Dissertation Improvement: Environmental Effects on Human Cranial and Postcranial Sexual Dimorphism

了解人类体型和颅面特征的环境可塑性将影响长期的人类进化研究，并可能用于测试人类性选择的行为心理学理论。更好地了解人类二态特征的性别特异性环境可塑性将提供有关生物和文化适应的信息，生物考古收集，以及推断考古种群所承受的环境压力的工具。记录人群在体型和颅面二型性方面的差异是在法医和生物考古环境中发展特定人群性别确定方法的关键。此外，3D表面扫描技术的使用提供了新的量化和存储机会，随着软件的进步，可以进行未来的分析，促进数据共享，并在研究人员无法亲自前往收集的情况下支持协作。该项目还将支持一名女研究生的培训和专业准备。影响现代人颅骨和颅骨后两性异形跨文化差异的因素尚不清楚。一些证据表明，雌性可能对环境压力有更好的缓冲，导致在恶劣条件下样本的体型二态性系统性下降。相比之下，颅面特征（如眉脊和下巴形态）的二态性被假设与配偶偏好和性选择有关，并且应该是环境中性的，甚至在恶劣的气候条件下会增加。然而，量化这种离散的颅面特征已被证明具有挑战性，传统定性方法的主观性妨碍了性别之间或跨人群的客观统计分析。本项目利用一种新的量化颅面特征形态的方法来研究颅面特征二态性和颅后尺寸二态性在不同环境应激因素下的关系。几何形态测量方法将使用三维激光表面扫描客观量化眉脊和下巴形态的两性二态性。这些颅面特征和骨骼尺寸的性别二态性将在一系列种族和文化多样化的人群中进行评估。在基因相关但环境不同的样本之间进行特定的比较，将被用来试图分离个体环境因素对颅后和颅后两性异形的影响。

Knowledge of the environmental plasticity of both body size and craniofacial traits in humans will impact long-term human evolutionary studies, and may be used to test behavioral psychology theories of human sexual selection. A better understanding of the sex-specific environmental plasticity of human dimorphic features would provide information regarding biological and cultural adaptations, bioarchaeological collections, and a tool to infer environmental stresses endured by archaeological populations. Documenting population variations in body size and craniofacial dimorphism is key to developing population-specific sex determination methods in forensic and bioarchaeological contexts. In addition, the use of 3D surface scanning technology provides new quantification and storage opportunities that allow for future analyses as software advances, facilitates data sharing, and supports collaboration in situations where researchers cannot physically travel to collections. The project will also support the training and professional preparation of a female graduate student. The factors influencing cross-cultural variation in modern human cranial and postcranial sexual dimorphism are not well understood. Some evidence suggests that females may be better buffered against environmental stressors, resulting in a systematic decrease in body size dimorphism in samples under poor conditions. In contrast, dimorphism in craniofacial traits such as brow ridge and chin morphologies has been hypothesized to be related to mate preference and sexual selection, and should be environmentally neutral or even increase under poor climatic conditions. Quantifying such discrete craniofacial traits, however, has proven challenging, and the subjectivity of traditional qualitative methods prevents objective statistical analyses between the sexes or across populations. This project utilizes a novel method of quantifying cranial trait morphologies to examine the relationship between craniofacial trait dimorphism and postcranial size dimorphism with various environmental stressors. A geometric morphometric method will be used to objectively quantify sexual dimorphism in brow ridge and chin morphologies using 3D laser surface scans. Sexual dimorphism in these craniofacial traits and skeletal measures of body size will be evaluated in an array of ethnically and culturally diverse populations. Specific comparisons between genetically related, yet environmentally disparate samples will be employed in an attempt to isolate the effects of individual environmental factors on postcranial and cranial sexual dimorphism.