QUANTIFYING SEXUAL DIMOPRHISM IN THE ADULT HUMAN CRANIUM Dissertation Presented in Partial Fulfillment of the Requirements for the Degree of Doctor of Philosophy in the Graduate School of The Ohio State University By Ana M. Casado Graduate Program in Anthropology The Ohio State University 2017 Dissertation Committee: Dr. Paul W. Sciulli, Advisor Dr. Samuel D. Stout, Co-Advisor Dr. Douglas Crews Copyright by Ana M. Casado 2017 ii ABSTRACT Biological anthropologists estimate sex from skeletal remains for forensic identification purposes or to reconstruct demographic profiles of past populations. Several features of the human cranium exhibit observable differences between males and females, known as sexual dimorphism. These sex-based differences are due to size disparities in muscle attachment sites as well as hormonal variations (Russell, 1985; Bass, 2005). A problem facing biological anthropologists is that of secular trends, or changes in physical traits over time; in the human skeleton. Most skeletal secular changes have been noted within the last 50 years (Jantz and Jantz, 1999, 2000). The most apparent secular trend is the increase in long bone length, and the consequent increase in height (Jantz and Jantz, 1999). Additionally, the human cranium has gotten taller and narrower, which can affect accurate sex estimation (Jantz et al., 2012). This research examines areas of the human skull that differ between the sexes and explores whether secular changes have affected sexually dimorphic areas of the cranium. The sample consists of 716 adult human crania of European European and African American ancestries from three skeletal collections: the Hamann-Todd Collection at the Cleveland Museum of Natural History, the Documented Skeletal Collection from the University of New Mexico’s Maxwell Museum, and the William M. Bass Donated Skeletal Collection housed at the University of Tennessee. The crania come from four defined generations, spanning birth years from 1864 to 1992. The ii individuals in the present sample were specifically chosen to fall between the ages of 20 and 60 to eliminate those who would not reflect pubertal changes and those who might show the most exaggeratedly robust cranial features in older age. To increase measurement accuracy, crania exhibiting fragmentation, trauma, or pathological conditions were not included. This dissertation includes skeletal samples from European American and African American individuals, and excludes crania of Hispanic, Asian, or any other ancestral affinity. The sample is limited to two groups due to underrepresentation of other populations in American skeletal collections. The six areas of the cranium analyzed here were specifically selected for their contribution to overall cranial robustness. These areas include: the external occipital protuberance, the nuchal area (or protuberances), the glabella, the mastoid processes, the supraorbital ridge(s) and frontal bossing. The novel measurement method proposed here quantitatively measures each trait (in millimeters), and considers the outward projection of each trait instead of the traditional method, which is to visually assess each feature and score its size and appearance on a scale of 1-5. To measure the cranial features, coordinate calipers were used, which provide an inexpensive and highly accessible alternative for three-dimensional skeletal data collection. Measurements were analyzed using a variety of statistical tests, including the measure of sexual dimorphism in a population, known as the calculation of D (after Bennett, 1981, and Chakraborty and Majumder, 1982). In addition, summary statistics, t- tests, analyses of variance, and discriminant function analyses were undertaken to test the hypotheses proposed in this dissertation. Results show that 12 features across the iii generations and ancestral groups exhibit sexual dimorphism (defined here as a D value of > 0.5). The sexual dimorphism associated with certain features, such as the supraorbital ridge, increased over the four generations, while the dimorphism associated with others stayed the same. No features experienced a decrease in sexual dimorphism over the four generations. From the discriminant function on the premodern dataset (Generations 1 and 2 combined), 77.8% of crania were correctly classified as males or females, a number which is roughly equivalent to the classification accuracy reported in most studies using traditional sex estimation methods. Only 51.1% of crania were correctly classified from the modern dataset (Generations 3 and 4 combined), and this may be because of secular trends affecting these areas of the cranium. Additionally, other discussions concerning changes in specific traits over time is included. Another two discriminant analyses were performed using the three traits exhibiting the highest levels of sexual dimorphism; classification accuracies were much higher for both premodern and modern datasets, and higher for premodern than the modern group of crania. This research is crucial for biological anthropologists and anatomists interested in skeletal change and human identification. Clearly, crania have changed over time, and the extent of those changes is somewhat quantified here, though more research is needed. As the modern human population changes, anthropologists must continue to improve their standards. This study will improve our understanding of cranial secular trends and will allow for more accurate skeletal identification. iv ACKNOWLEDGMENTS I wish to thank those who allowed me to access the skeletal collections used for this dissertation: Lyman Jellema, of the Cleveland Museum of Natural History, Dawnie Wolfe Steadman of the University of Tennessee’s Bass Collection, and Heather Edgar, of the Maxwell Museum at the University of New Mexico. I would also like to thank the members of my committee for advice and comments along the way, especially statistical advice. Special thanks to Meng Li and Stacy Porter for statistical guidance. Samantha Blatt, thank you for the beautiful drawings to supplement my method descriptions. Thanks to James Roberts, for supporting me and being willing to put up with the odd and hectic schedule of a graduate student. Y para Ben: Mi vida ha sido por tí. v VITA May 2003 .......................................................Farragut High School 2007................................................................B.A. Anthropology, University of Tennessee 2010................................................................M.A. Anthropology, The Ohio State University Publications Casado AM. 2017. Quantifying Sexual Dimorphism in the Human Cranium: A Novel Method. Journal of Forensic Sciences Fields of Study Major Field: Anthropology vi Table of Contents ABSTRACT ....................................................................................................................... ii ACKNOWLEDGMENTS ................................................................................................ v VITA.................................................................................................................................. vi List of Tables .................................................................................................................... ix List of Figures ................................................................................................................... xi CHAPTER 1 – INTRODUCTION .................................................................................. 1 Background: Literature Review and Previous Research .......................................... 1 Sexual Dimorphism: An Overview .............................................................................. 1 Causes for sexual dimorphism ..................................................................................... 2 Proximate Causes, or Extrinsic Factors for Sexual Dimorphism ......................... 3 Ultimate Causes, or Intrinsic Factors for Sexual Dimorphism ............................. 5 Measuring Sexual Dimorphism ................................................................................... 7 Sexual Dimorphism in the Human Skeleton ............................................................... 8 Sexual dimorphism in the human pelvis.................................................................. 9 Sexual dimorphism in the long bones .................................................................... 13 Sexual dimorphism in the human cranium ........................................................... 13 Sexual Dimorphism Across Populations................................................................ 15 Biological Ancestry and the Human Cranium ...................................................... 17 Sexual Dimorphism and Age-At-Death ................................................................. 19 Environmental Effects on the Human Cranium ...................................................... 21 Climate ...................................................................................................................... 21 Nutrition ................................................................................................................... 23 Mastication ............................................................................................................... 24 Growth and Development of the Human Cranium ................................................. 25 Cranial growth ........................................................................................................