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birthdates in the nineteenth century were obtained from the Hamann-Todd Human Oste-
ological Collection 3 and the Robert J. Terry Anatomical Skeletal Collection while twentieth
century samples were obtained from the Forensic Databank. Given that these collections
are composed of known individuals, sex, ancestry, and birth year were available for all
individuals. Data were subjected to Procrustes superimposition and multivariate regression
was performed on the partial warp scores based on TPS. They found the most prominent
change is associated with the cranial base for both groups. The authors concluded that
proximate causes for this change are associated with the rapid neural growth trajectory
of the basicranium in early development or growth rate allometry. Ultimate causes for
these changes, the authors posit, are associated with improved health and nutrition.
Kimmerle and Jantz (2005) studied secular trends in asymmetry by analyzing craniofacial
traits in a large sample of Euro- and African-Americans born between the years 1820 and
1980. Building on previous research for cranial morphological secular trends within this
dataset, these authors tested the possible relationship for increased asymmetry during
periods of rapid morphological change. Seven bilateral landmarks were chosen for their
analysis. Coordinate data were subjected to GPA and differences in asymmetry were
assessed through a MANOVA. Centroid Size was used for analyses of size asymmetry.
Two-way ANOVAs were performed to test for the main effects of side to test for directional
asymmetry (the propensity for a particular side of a trait to develop more than the other),
individual, and the interaction between side and individual on size and shape for both
sex and ancestral groups. Fluctuating asymmetry (subtle deviations that exist between paired
structures due to random perturbations of developmental processes) over time was assessed
via regression analysis.
The only group to exhibit some degree of developmental instability was African American
females. The interpretation of developmental instability is challenging given the various
genetic and environmental components that might result in the observed asymmetry. Inter-
estingly, not all American samples showed a significant degree of fluctuating asymmetry as
might be expected from such vast environmental change during the period under study.
Nineteenth century America saw many environmental changes for African Americans,
including nutritional deficiencies, infectious disease, and parasitic load as well as detrimental
social conditions (i.e., segregation and social discrimination). The authors conclude that
perhaps a combination of the effects of slavery, the American Civil War, Reconstruction,
and the Depression in the Southern United States had a significant effect on cranial asymme-
try. This study not only illustrates the efficacy of geometric morphometrics for studying
shape change through time, but it also reminds us that biological variation is the product
of both genetics and environment acting on the phenotype and that social conditions and
stress are components of environmental factors (e.g., see Gravlee, 2009 ).
Weisensee and Jantz (2011) examined secular change in cranial morphology in the New
Lisbon collection, a documented skeletal collection from Lisbon, Portugal with birth years
ranging from 1806 to 1954. This period represents significant changes in the population,
including increased urbanization, population growth, and changes in mortality and fertility
patterns. As this population is from a more geographically restricted space compared with
3 This collection is curated by the Cleveland Museum of Natural History in Cleveland, Ohio.
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