Research by economists suggests that recent Mexican migrants are better educated and have higher socioeconomic status (SES) than previous migrants. Because factors associated with higher SES and improved education can lead to positive secular changes in overall body form, secular changes in the craniofacial complex were analyzed within a recent migrant group from Mexico. The Mexican group represents individuals in the act of migration, not yet influenced by the American environment, and thus can serve as a starting point for future studies of secular change in this population group. The excavation of a historic Hispanic cemetery in Tucson, Arizona, also allows for a comparison between historic Hispanics and recent migrants to explore craniofacial trends over a broad time period, as both groups originate from Mexico.

The present research addresses two main questions: (1) Are cranial secular changes evident in recent Mexican migrants? (2) Are historic Hispanics and recent Mexican migrants similar? By studying secular changes within a migrant population group, secular trends may be detected, which will be important for understanding the biological variation of the migrants themselves and will serve as a preliminary investigation of secular change within Mexican migrants. The comparison of a sample of recent Mexican migrants with a historic Hispanic sample, predominantly of Mexican origin, allows us to explore morphological similarities and differences between early and recent Mexicans within the United States.

Vault and face size and a total of 82 craniofacial interlandmark distances were used to explore secular changes within the recent Mexican migrants (females, n = 38; males, n = 178) and to explore the morphological similarities between historic Hispanics (females, n = 54; males, n = 58) and recent migrants. Sexes were separated, and multivariate adaptive regression splines and basis splines (quadratic with one knot) were used to assess the direction and magnitude of secular trends for the recent Mexican migrants. Because dates of birth were unavailable for the historic sample, partial least squares discriminant analysis (PLS-DA) was used to evaluate morphological differences between historic and recent Mexican migrant samples. The data were separated into a training data set and a testing data set to ensure realistic results.

Males had eight variables (four positive and four negative) and females had six variables (two positive and four negative) that demonstrated significant differences over time. In the PLS-DA, three components were identified as important in model creation and resulted in a classification accuracy of 87% when applied to a testing sample. The high classification accuracy demonstrates significant morphological differences between the two groups, with the historic Hispanic sample displaying overall larger craniofacial dimensions.

While differences in cranial morphology are evident between historic Hispanics and recent Mexican migrants, relatively few positive and negative secular trends were detected within the recent migrant sample.

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 occurred 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.

Over the past two centuries there have been documented secular changes in stature, weight, body proportions, and skeletal maturation rates in the United States. These changes along with a more sedentary lifestyle are likely reflected in femur morphology. Here we examine secular changes in diaphyseal cross-sectional size, shape, area, robusticity, and rigidity at midshaft and subtrochanteric of the femur using 395 adult white females and males from the United States born between the 1850s and the 1970s. The effect of secular change was controlled for an age effect. We also examine the relationship between femur length (proxy for stature) and femur head diameter (proxy for body weight) on measurements of diaphyseal size and biomechanical properties. The femur morphology of Americans born in the twentieth century reflects the combination of changes in stature, body build, and activity levels. Both sexes show significant changes in femur midshaft shape due primarily to a decrease in the mediolateral diameter. There are no significant changes at subtrochanteric in size or biomechanical properties in either sex after controlling for age variation. The results suggest that the changes in femur midshaft shape are primarily associated with a decrease in activity. The stability of the subtrochanteric dimensions and femur anteroposterior diameter may reflect a combination of decreased activity with a corresponding increase in femur length (moment arm) and a decrease in body breadth.

Osteometric measurements of the femur are consistently used to estimate stature, sex, and race in constructing demographic profiles. The presence of positive or negative changes in the size of the maximum vertical diameter of the femoral head could potentially affect the validity of such profiles. Additionally, changes in femoral head size may be an indicator of the socioeconomic status, health, and nutrition of a population over periods of time. Two large data sets consisting of white male and white female femoral vertical head diameter measurements with birth years spanning 1841–1990 are used in this study. A combination of both LOESS and piecewise regression models determined the presence of secular changes in femoral head size. Tests of the residuals were also conducted to assess normality of the data and goodness of fit of the nonlinear models. The results indicate that white males and females experienced nonsignificant increases in femoral head diameter size before 1920 and significant decreases in size thereafter. The results of this study are consistent with other studies that have identified changes in body and skeletal morphology. Considerable changes and improvements in environmental conditions that humans have experienced since the mid-nineteenth century likely contribute to the decrease in femoral head size observed in this study.

Secular changes in stature, weight, or other components of the body that can be obtained from historical records have been extensively studied. Cranial change has been central to anthropology for more than a century, but the focus has normally been on change measured in centuries or millennia. Cranial change measured in decades, normally considered to result from plastic response to the environment, has been less studied. This article reports on change in cranial vault dimensions in white Americans.

Variables were glabello-occipital length (GOL), basion-bregma height (BBH), basion-nasion length (BNL), maximum cranial breadth (XCB), and biauricular breadth (AUB). Cranial size was calculated as the geometric mean of these variables, and shape dimensions were calculated as described by Darroch and Mosimann (1985). Cranial module and cranial capacity were also calculated. Samples consisted of 1,112 males and 668 females complete for those variables. Samples were organized into 10-year birth cohorts, with birth years ranging from 1820 to 1990. One-way ANOVA was used to test for variation among cohorts. The pattern of secular change was examined graphically and was compared with quality-of-life and environmental indicators, including stature, infant mortality, calories per person, and relative number of immigrants.

All variables showed significant secular change, but BBH, XCB, and BNL responded most strongly. Over the past 170 years, crania became relatively higher, narrower, and larger with longer cranial bases. Both sexes changed, but female change was less pronounced than male change. The cranial variables tracked secular changes in stature, most prominently BNL. The highest correlation between a cranial variable and quality-of-life indicator was BBH and infant mortality.

We are not able to identify specific causes of secular changes in cranial morphology. However, given that modern Americans have introduced themselves into a novel environment never before experienced by human populations, we consider it unlikely that it is pure plasticity. In addition to possible plastic responses, it is likely that selection, acting through the dramatic changes in infant mortality, is also involved.

Secular change in height has been extensively investigated, but size and shape of the postcranial skeleton much less so. The availability of large, documented collections of nineteenth- and twentieth-century skeletons makes it possible to examine changes in skeletal structure over the past 150 years. We examined secular changes in long bone lengths and proportions, their allometric relationship to stature, and crosssectional properties of long bone shafts. Bone measurements and stature were organized into 10-year birth cohorts, ranging from 1840 to 1989. Variation among cohorts was tested by one-way ANOVA, and secular trend was examined visually by plotting mean measurements by birth decade. Allometry was examined by regressing log bone lengths onto log stature, using least squares regression. Allometry was also examined using the geometric mean of log bone lengths as the size variable. All bone lengths and stature showed positive secular change. Stature and the distal long bones showed the most pronounced changes. Proportions also changed, as revealed by the brachial and crural indices. Both indices increased, but the brachial index change was the most pronounced. Allometric relationships suggest that brachial index changes result from positive allometry of the radius and negative allometry of the humerus. Similar but less marked allometric relationships were found in the tibia and femur. Long bone shaft properties changed in the following ways: femur midshafts and tibia shafts at the nutrient foramen became more mediolaterally narrowed, and the femur became more mediolaterally thickened at the subtrochanteric level, approaching platymeria. All major long bones became more gracile. These remarkable changes in the postcranial skeleton are a response to the unparalleled changes in the environment in which modern Americans now live. Changes in growth resulting from plentiful and secure nutrition, reduced disease load, and marked reduction in bone loading from reduced activity levels are mainly responsible.

Secular changes refer to short-term biological changes ostensibly due to environmental factors. Two well-documented secular trends in many populations are earlier age of menarche and increasing stature. This study synthesizes data on maximum clavicle length and fusion of the medial epiphysis in 1840–1980 American birth cohorts to provide a comprehensive assessment of developmental and morphological change in the clavicle.

Clavicles from the Hamann-Todd Human Osteological Collection (n = 354), McKern and Stewart Korean War males (n = 341), Forensic Anthropology Data Bank (n = 1,239), and the McCormick Clavicle Collection (n = 1,137) were used in the analysis. Transition analysis was used to evaluate fusion of the medial epiphysis (scored as unfused, fusing, or fused). Several statistical treatments were used to assess fluctuations in maximum clavicle length. First, Durbin-Watson tests were used to evaluate autocorrelation, and a local regression (LOESS) was used to identify visual shifts in the regression slope. Next, piecewise regression was used to fit linear regression models before and after the estimated breakpoints. Multiple starting parameters were tested in the range determined to contain the breakpoint, and the model with the smallest mean squared error was chosen as the best fit. The parameters from the best-fit models were then used to derive the piecewise models, which were compared with the initial simple linear regression models to determine which model provided the best fit for the secular change data.

The epiphyseal union data indicate a decline in the age at onset of fusion since the early twentieth century. Fusion commences approximately four years earlier in mid- to late twentieth-century birth cohorts than in late nineteenth- and early twentieth-century birth cohorts. However, fusion is completed at roughly the same age across cohorts. The most significant decline in age at onset of epiphyseal union appears to have occurred since the mid-twentieth century. LOESS plots show a breakpoint in the clavicle length data around the mid-twentieth century in both sexes, and piecewise regression models indicate a significant decrease in clavicle length in the American population after 1940. The piecewise model provides a slightly better fit than the simple linear model. Since the model standard error is not substantially different from the piecewise model, an argument could be made to select the less complex linear model. However, we chose the piecewise model to detect changes in clavicle length that are overfitted with a linear model.

The decrease in maximum clavicle length is in line with a documented narrowing of the American skeletal form, as shown by analyses of cranial and facial breadth and bi-iliac breadth of the pelvis. Environmental influences on skeletal form include increases in body mass index, health improvements, improved socioeconomic status, and elimination of infectious diseases. Secular changes in bony dimensions and skeletal maturation stipulate that medical and forensic standards used to deduce information about growth, health, and biological traits must be derived from modern populations.