An Examination of the Differential Effects of the Modern Epidemiological Transition on Cranial Morphology in the United States and Portugal

This research examines the pattern of secular change in the cranial morphology of two populations experiencing the epidemiological transition associated with decreased mortality rates in children, followed by declines in infant mortality and subsequent increases in adult longevity. The two samples examined in this study come from US and Portuguese individuals. The epidemiological transition oc- curred at different times in the United States and Portugal, with Portugal entering into the transition later than the United States. The results of the study show that the US and Portuguese samples experienced significant changes in cranial morphology during the approximately 150 years under study. In all of the samples the cranial base morphology changes significantly over time. However, the pattern of change in the US and Portuguese samples varies in the other regions of the crania. The US samples exhibit significant changes associated with the posterior cranial fossa, which experiences the greatest growth during the fetal period and the first year of life. Conversely, in the Portuguese samples the region of the cranium that shows the greatest change is in the face and lateral cranial base, which experiences the greatest growth from three to nine years. This differential pattern may reflect differences in changing mortality patterns in the two countries. During the period under study the United States had already proceeded through the early stages of the epidemiological transition, and improvements in the juvenile mortality and juvenile growth had occurred previously. Subsequently, the United States experienced significant declines in infant mortality, and the regions of the crania that exhibit the greatest changes occur in area with maximum growth velocity under one year. However, Portugal entered into the epidemiological transition later than the United States and therefore the greatest changes in growth occurred during the juvenile period, which is reflected in the adult morphology in this group. This study demonstrates the utility of variation in growth patterns in different cranial regions to document changes in the demographic parameters in two different populations

Exploring the Relative Importance of Spatial and Environmental Variation on the Craniometrics of the Modern Portuguese

Previous research on the causes of craniometric variation within and among human populations has invoked both genetic and environmental explanations. Recent studies of modern populations in the United States and Portugal, among other populations, suggest that changes in environmental conditions have resulted in significant changes in cranial morphology. While similar changes in cranial morphology have been observed in genetically diverse populations, these populations do not appear to be converging on a common form. This study seeks to understand the role that population history and environmental variation play in explaining craniometric variation in the modern Portuguese. Using three-dimensional craniometric data collected from an identified skeletal collection from Lisbon, Portugal, this research examines the relationship between cranial morphology and place of birth. Two hypotheses are tested with regard to craniometric variation. The first asks whether phenotypic variation is related to geographic distance in the sample and therefore accurately represents genetic relationships. The second explores whether the significant secular changes observed in the sample obscure the population history reconstructed using craniometric data. The results demonstrate a significant relationship between geography and cranial morphology in the modern Portuguese sample. The clinal distribution to the craniometric variation is similar to what has been reported in some studies of molecular DNA from the Portuguese. The results show that cranial morphology reflects both the geography and genetic history of the sample and, furthermore, that secular changes in the population neither obscure nor erase this pattern. This study illustrates that even when secular changes have a significant impact on cranial morphology, they do not impede researchers’ ability to reconstruct genetic relationships using craniometric data