Secular change has been documented in a number of studies focused on cranial and postcranial morphometrics and nonmetric traits. However, to date, few studies have addressed the potential of temporal change occurring in the expression of cranial nonmetric traits utilized in ancestry estimation. This study examines the effect of secular change on the expression of 23 cranial and mandibular nonmetric traits frequently employed in ancestry estimation; with age-at-death, sex, and year-of-birth of each individual documented for data analysis. Data were collected from European American individuals from the Hamann-Todd Skeletal Collection (n=518) and from the William M. Bass Donated Skeletal Collection (n=602). Individuals were divided into birth-year cohorts as follows: Hamann-Todd Skeletal Collection: 1824-1849 (Cohort 1), 1850-1874 (Cohort 2), 1875-1899 (Cohort 3), and 1900-1924 (Cohort 4); William M. Bass Donated Skeletal Collection: 1900-1924 (Cohort 4), 1925-1949 (Cohort 5), and 1950-1987 (Cohort 6). Pearson’s chi-square analyses produced significant p-values (≤ 0.01) in 19 of the 23 traits between the six birth-year cohorts. Factor maps generated through correspondence analyses were used as visual representations of relative trait expression between the cohorts. Ordinal regression analyses assessed the degree of variation between each cohort in relation to Cohort 1 along with the influence of age-at-death and sex on trait expression. Overall, analyses of the data revealed that secular change has occurred in 11 of the 23 traits, including: anterior nasal spine (ANS), malar tubercle (MT), nasal bone contour (NBC), postbregmatic depression (PBD), supranasal suture (SPS), transverse palatine suture (TPS), zygomaticomaxillary suture (ZS), gonial angle flare (GAF), mandibular tori (MDT), and posterior ramus edge inversion (PREI). Change in trait expression occurred in both males and females in seven traits, including: ANS, MT, TPS, ZS, GAF, MDT, and PREI. Significant change in trait expression occurred predominately between Cohorts 3 and 4 (birth years ranging from 1875 to 1924) and Cohorts 4 and 5 (birth years ranging from 1900 to 1949). This study demonstrates that secular change in nonmetric cranial and mandibular traits has occurred over the last two centuries with the greatest change appearing at the turn of the twentieth century.

The human bony pelvis has evolved into its current form through competing selective forces. Bipedalism and parturition of large headed babies resulted in a form that is a complex compromise. While the morphology of the human pelvis has been extensively studied, the changes that have occurred since the adoption of the modern form, the secular changes that continue to alter the size and shape of the pelvis, have not received nearly as much attention. This research aims to examine the changes that have altered the morphology of the human bony pelvic girdle of individuals in the United States born between 1840 and1981. Secular changes in the human skeleton have been documented. Improvements in nutrition, decreased disease load, exogamy, activity, climate, and other factors have led to unprecedented growth in stature and weight. The size and shape of the pelvic canal, os coxa, and bi-iliac breadth were all examined in this study. Coordinate data from males and females, blacks and whites were digitized. Calculated inter-landmark data was analyzed using traditional metric methods and the coordinate data was analyzed using 3D geometric morphometrics. After separating the samples into cohorts by sex and ancestry, results indicate that there is secular change occurring in the modern human bony pelvis. Changes in shape are significant across the groups while only white males exhibit increases in size. The dimensions of the pelvic canal have changed over time. The birth canal is becoming more rounded with the inlet anteroposterior diameter and the outlet transverse diameter becoming longer. These diameters, once limiters, are believed to have led to an adoption of the rotational birth method practiced by modern humans. In addition, the bowl of the pelvis is becoming less flared. Childhood improvements in nutrition and decreases in strenuous activity may be the cause of the dimension changes in the bony pelvis. The similar changes across both sexes and ancestries indicate a similar environmental cause. However, it is likely a combination of factors that are difficult to tease apart. Whether the increases continue remains to be determined.

The use of geometric morphometrics (GM) in physical anthropology has increased markedly over the recent years. In current studies of secular change, anthropologists have more frequently turned to this technique as it provides scientists with a powerful tool for shape analysis. Secular change is defined as changes in the skeletal biology, usually seen in a population, resulting from shifts in living standards or exposure to a new environmental factor over a short timeframe (Jantz and Meadows Jantz 2000; Weisensee and Jantz 2011). Studies conducted in Europe, Asia, and the United States have shown significant signs of secular change in craniofacial morphology. This thesis will utilize GM analyses of 57 craniofacial landmarks from 313 individuals to determine secular change in the European male populations of the Raymond A. Dart and Pretoria Skeletal Collections located in Johannesburg and Pretoria, South Africa, respectively, with birth years ranging from 1850 to 1956. Craniofacial data points were collected using a 3D Microscribe digitizer, upon which the Generalized Procrustes Analysis (GPA) was used to align all landmarks into one coordinate reference plane. In order to determine the presence of shape change, a Principal Components Analysis (PCA) was run on the Procrustes coordinates of all individuals. Then, a multivariate regression of shape score on year of birth was conducted to determine the magnitude of change as explained over time. Following the multivariate regression, various Canonical Variates Analyses (CVA) were performed to determine whether secular change was occurring. In addition to collecting metric data, ultimate and proximate causes are explored to provide a more holistic understanding of the potential reasons for the changing or unchanging nature of the crania in the ancestrally European South African population. This study hypothesizes these collections will exhibit craniofacial secular change resulting from greater exposure to increased nutrition over time, greater access to healthcare, and socioeconomic and political stability. Additionally, genetic factors could be affecting the development of the crania through time. As many studies use the Dart and Pretoria collections in tandem to understand population-specific traits of modern South Africans, the presence of secular change will greatly affect the way researchers utilize samples for their studies. Forensic anthropologists study collections to create better estimations for elements of the biological profile such as stature, age, and sex. However, failure to take into account secular change would provide erroneous results. This study provides answers regarding the need to account for secular change if necessary. This research indicates that there are some changes occurring in the craniofacial morphology as see by the PCA, but the results of the CVA indicate that this is not necessarily due to secular change. The results do not clearly indicate the presence of secular change. There are many possibilities dictating potentially why. The first possibility is that there are small changes occurring in the craniofacial morphology; however, this is not caused by secular change. There are other variables, potentially genetic, that are influencing these slight changes that we see. Despite other nations with similar economic development trajectories experiencing a definite presence of secular change, the unique history and population structure of European South Africans could be contributing to the lack of secular change present. Another possible reason is the lack of passage of time from the industrialization of the nation. Furthermore, there is potentially not enough data tested to warrant a reliable conclusion that secular change is or is not occurring. With the cranium, the possibility exists that a minimum threshold of specimens is needed in order to have a reliable conclusion.