The Effect of Novel Environments on Modern American Skeletons

The articles in this special issue describe secular change analyses that were presented at a symposium held at the 2012 meeting of the American Association of Physical Anthropologists. The purpose of the symposium was to present and synthesize findings on the secular changes in American skeletal morphology over the last 100–200 years and to identify new directions such research might take. This special issue includes research on populations other than modern Americans to provide a comparative context and to highlight the remarkable changes that have occurred solely in the United States. Most of the data come from the cranial vault and lower extremity. Ideally, we would like to examine the influence of specific environmental factors on different components of the skeleton. Although our understanding of causes is not sufficiently developed in the current state of the field to permit such an approach, the authors offer thought-provoking hypotheses about the results of their analyses.

More than 100 years ago Franz Boas (1911) investigated American environmental effects through immigrants and their families using several anthropometrics. His results demonstrated not only that head shape changes within families could be quite dramatic from one generation to the next but also that the different ethnic groups responded differently to immigration. The analyses in this special issue use data from skeletal collections from the American population and comparative samples from other countries to provide insight into changes in American skeletons over two centuries. Information such as birth year, ethnicity, nationality, numerous anthropometrics, occupation, and cause of death is documented in these collections. Studying the entire skeleton allows the breakdown of stature into component upper and lower body dimensions and the assessment of size, shape, and robusticity changes in various areas of the skeleton.

Most of the research into secular changes has focused on stature and weight and has been conducted by economic historians on populations worldwide since 1800. These studies have illustrated how those variables change with changing economic, political, medical, sanitary, disease, and exercise conditions and in relation to direct measures of overall health, such as infant mortality and life expectancy. Changes in many Western countries have progressed similarly, but in the United States the events and changes from 1800 to the present were unique, owing in part to its large expanse and geographic and political isolation from Europe. Some aspects of human biological responses to the remarkable changes in American standard of living and economic well-being since the turn of the twentieth century have been thoroughly reported and analyzed by Fogel (2004) and Floud et al. (2011). These works are based mainly on historical measurements of the living and are mostly limited to height and weight or indices derived from them, such as body mass index. Changes in these anthropometric variables over the past few centuries, reflecting changes in health and well-being, form the core of the relatively new field of anthropometric history (Ulijaszek and Komlos 2010). Although informative, stature and weight tell only part of the story.

Skeletons possess some advantages over historical statures in establishing relationships between biological and environmental variables, an observation Trotter and Gleser (1951) made long ago. Chief among them is the ability to decompose a composite measure like height into its individual components and to examine changes in body proportions (Meadows and Jantz 1995): relatively longer legs are seen in taller people and can be the product of better early childhood growth, when the legs grow faster than the trunk. It is also possible to examine changes in specific structures such as the skull and pelvis, which is impossible through historical records. Markers of activity and obesity can also be examined (Moore 2008; Ruff et al. 1991; Shaw and Stock 2009; Wescott 2006), and indicators of possible changing genetic affinities and composition can be examined, such as skeletal and dental nonmetric traits (Ousley and Edgar 2012). In essence, examination of the complete skeleton provides a finer-grained picture and hence provides greater insight into the nature of the biological changes the American population...