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Age at the initiation of puberty and at menarche are key maturational indicators. They reflect health both within and between populations; in that a declining average age is associated with improving health, nutrition, and socio-economic conditions. Knowledge of the timing of pubertal development and menarche is important as earlier development within a population, in particular, has been linked with an increased risk of negative sequelae including overweight and obesity, development of risk factors for non-communicable diseases such as hypertension and insulin resistance, and engagement in risk behaviours such as early sexual debut and substance abuse. The main aims of this study were to investigate the timing of, and the early life factors (such as body composition and growth velocities) associated with pubertal development and age at menarche in Black and White urban South African adolescents. Mixed-longitudinal data (n = 401) from the Birth to Twenty (Bt20) birth-cohort study, initiated in 1990 and set in SowetoJohannesburg, South Africa were used. Median age at the initation of puberty and at menarche was derived by fitting logistic curves to cumulative frequency plots. Logistic regression models were constructed to examine the early life predictors of the timing of puberty and menarche. Data were also collected from adolescents and Bt20 staff (n = 72) using focus groups to explore views on the pubertal development questionnaire used in the Bt20 study. Median age at the initiation of genitalia development was 10.4 years (95% Cl = 8.4, 12.4) for Black boys and 9.8 years (95% Cl = 9.4, 10.2) for White boys. Median age for the initiation of pubic hair development for Black males was 10.8 years (95% Cl = 9.6, 12.0) compared to White males, which was 10.2 years (95% Cl = 8.4, 12.0). Median age at the initiation of breast development in Black females was 10.1 years (95% Cl = 9.3, 10.9) compared to White females which was 10.2 years (95% Cl = 8.2, 12.2). Median age for the initiation of pubic hair was 10.3 years (95% Cl = 9.3, 11.3) and 10.5 years (95% Cl = 8.7, 12.3) for Black and White girls, respectively. Results from logistic regression showed that a greater weight and height velocity in late childhood significantly increased the odds of achieving early breasU genitalia development. Furthermore, a low socio-economic status (SES) index at 9/10 years significantly reduced the odds of achieving early breasUgenitalia development. A greater weight, height, body mass index (BM I), and growth rate during infancy and childhood significantly increased the odds of achieving early pubic hair development. Median age at menarche for Black females was 12.4 years (95% Cl = 12.2, 12.6) and 12.5 . years (95% Cl = 11.7,13.3) for White females. Average menarcheal age for Black girls has declined by 0.56 years per decade and 0.32 years for White girls in South Africa, when comparing the current study findings with those from previous studies. Results from logistic regression showed that being taller, fatter and heavier in late childhood significantly increased the odds of achieving earlier menarche. The focus groups provided a range of opinions relating to the Bt20 pubertal development questionnaire and procedure. The majority of views were positive and included the ease of understanding and completion of the tool. Negative views revolved around the language used and privacy issues. These qualitative results provided a unique insight into the way in which pubertal development data are assessed and how these methods can potentially be improved to enhance the reliability and accuracy of pubertal development data collection. The results from this study provide the most recent estimates of age at the. initiation of puberty and age at menarche for urban Black and White South African adolescents. This is particularly important given the social, nutritional, and economic transition currently occurring in this country as these key maturity indicators reflect population health. This study has also added to our knowledge of the factors that are associated with pubertal development, showing that proximate rather than distal factors are the most sensitive indicators in this urban transitioning environment. In addition, the results from the focus groups provided a unique insight into how pubertal development data are assessed and how these methods could be improved. The negative health outcomes which have been associated with earlier pubertal development and age at menarche are major public health concerns, particularly in the South African context given the HIV/AIDS epidemic and rising levels of obesity. This study highlights the need for renewed research and resources for intervention strategies and policy programmes which target appropriate sex and obesity education in urban South African children.

Prior research has identified that the cranial vault has become taller and narrower and the mandible has decreased in breadth and become longer over time among Americans (Angel, 1976; Jantz and Meadows Jantz, 2000; Jantz, 2001; Martin and Danforth, 2009; Jantz and Meadows Jantz, 2016). Studies of the cranial vault also suggest narrowing of the face. However, research investigating secular changes in craniofacial morphology is lacking. Because the cranium is a complex of integrated modules with different trajectories and patterns of ontogeny and development, modular accommodation during growth is critical for the cranium to maintain functionality as a unit. This dissertation utilizes craniometric data from documented 19th and 20th century skeletal collections to investigate whether changes in craniofacial morphology have occurred concomitantly with those of the vault, and if so, whether those changes are related to changes in cranial base shape.Geometric morphometric analysis was performed using 21 digitized craniometric landmark data from a sample of n=662 White males and females. Generalized Procrustes Analysis was utilized to fit the three-dimensional coordinate data into a common coordinate system for the execution of further multivariate analysis. Principal components analysis and canonical variates analysis were executed to ascertain the presence of secular changes in craniofacial and base shape. Subsets of the 21 craniometric landmarks were analyzed to facilitate separate examinations of the face and base.Two-dimensional interlandmark distance data obtained from the same individuals were analyzed using correlation analysis, principle components analysis, and regression to corroborate the results of the geometric morphometric analysis. The use of non-traditional craniometric measures proved instrumental for identification of specific areas and directions of shape change.Lastly, a series of traditional cranial angle data obtained from a larger sample of n= ~1,500 individuals were analyzed using regression analysis. The examination of the cranial angle data served to substantiate the results obtained from the prior analysis and to further delineate secular changes in morphology.Results suggest that the faces of American White males and females have become more leptoprosopic (tall and narrow) and the cranial vault has become more dolichocephalic (longer and narrow) over time.

Introduction: Improved environments in the U.S. have resulted in taller, larger, and heavier children and adults compared to past generations. Studies of other skeletal-dental dimensions have shown increases across generations, and our perception is that teeth now are forming faster. The purpose of this study is to test for a secular trend towards faster tempos of tooth mineralization in a sample of U.S. white adolescents over the past quarter century (1980-85 to 2005-10). Materials: Two cohorts of 200 children each were identified, each with an age range of 10-to- 15 years, one group from 1980-85 and the more recent group from 2005-10. Children all were phenotypically normal American whites from the same dental clinic. Stages of tooth mineralization were scored for the lower 8 permanent tooth types using the 8-grade Demirjian system (Demirjian A, Goldstein H, Tanner JM. A new system of dental age assessment. Hum Biol 1973;45:211-27). Proportional hazards analysis was used to test for cohort differences while controlling for sexual dimorphism in tooth formation tempos. Results: In the age interval studied, 10 tooth-stage combinations could be analyzed statistically. Median ages of the stages were characteristically younger in the recent (2005-10) cohort, and 5 of these 10 comparisons achieved statistical significance (P < 0.05). The difference between the cohorts is larger in girls than in boys. Faster tempos of development are on the order of ½ year. Conclusion: Faster growth tempos mean that age-sensitive procedures—such a serial extraction or harnessing adolescent growth—occur at younger ages and that published standards for tooth formation and emergence probably now are biased. Faster maturation also suggests that children of the same chronological age are biologically more mature than in the past. It remains to be seen how widespread these secular quickenings are, both geographically and across segments of the population.