Examining plastic adaptive responses in the generation of human skeletal variation

点击翻译按钮获取中文摘要

Evolutionary models for skeletal morphology often apply “form follows function” explanations, focusing on the selective context of adult morphology. But, adult skeletal form is the product of the processes of growth and development, which are themselves subject to selection, and to environmental influences. Due to biological plasticity, human skeletal variation reflects, in part, differences in environmental (climate, terrain), ecological (resource availability, disease load), and lifestyle (diet, activity, technology) contexts. Challenging environments, with nutritional or dietary limitation, high activity budgets, or high parasitic or infectious disease loads lead to restricted skeletal growth, often leaving signatures in bone and dental tissues preserving evidence of these developmental stressors. Habitual activities load bones through body weight and muscle action and alter bone tissue distribution in the shafts of limb bones. As such, skeletal morphology can offer insights on evolutionary processes shaping our species, and factors affecting populations and individuals. But given the plasticity of skeletal tissue, these may not be the only ways in which these processes influence skeletal morphology during development. Joint regions of bones are thought to be tighty controlled during development by genetic factors and less responsive to the environment, suggesting their form should be more stable. Yet, ankle orientation varies in relation to substrate use, and the vertebral canal varies with stress. Plasticity exists in these regions. This research will use 3D geometric morphometric approaches to examine the size and shape characteristics of bones of the limbs and vertebrae in archaeologically derived human skeletal samples in relation to traditional skeletal indicators of developmental stress and habitual activity, to elucidate whether and how stress and activity during ontogeny can influence morphology. Anthropologists assume the morphology of extinct hominins largely reflects their evolutionary history as a product of normal growth, rather than plastic responses to environmental stressors. But in order to decipher the meaning of morphological variation in the fossil record we must understanding how plastic adaptive responses generate skeletal morphology. This is also important for bioarchaeologists, who employ outcomes of growth processes as indicators of population health through time in response to demographic and ecological changes. My research represents a novel approach to examining the influence of environment and activity in producing skeletal variation in humans. Understanding the interplay between plasticity and constraint (evolutionary, functional, developmental) in the generation of morphological variation in a species aids in identifying factors (environmental, ecological, lifestyle) that influence adaptation, which are of particular importance to evolutionary anthropologists, paleoanthropologists, and evolutionary anatomists.