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- All Subjects: Dental anthropology
- Creators: Schwartz, Gary T.
- Resource Type: Text
Description
Bioarchaeologists often use dental data and spatial analysis of cemeteries to infer the biological and social structure of ancient communities. This approach is commonly referred to as biological distance (“biodistance”) analysis. While permanent crown data feature prominently in these efforts, few studies have verified the accuracy of biodistance methods for recognizing child relatives using deciduous teeth. Thus, as subadults comprise an essential demographic subset of mortuary assemblages, deciduous phenotypes may represent a critical but underutilized source of information on the underlying genetic structure of past populations. The goal of the dissertation is to quantitatively analyze the developmental program underlying deciduous phenotypes and to evaluate their performance in accurately reconstructing known genealogical relationships. This project quantifies morphological variation of deciduous and permanent tooth crowns from stone dental casts representing individuals of known pedigree deriving from three distinct populations: European Canadians, European Australians, and Aboriginal Australians.
To address the paucity of deciduous-focused validation research, phenotypic distances generated from the dental data are subjected to performance analyses (biodistance simulations) and compared to genetic distances between individuals. While family-specific results vary, crown morphology performs moderately well in distinguishing relatives from non-relatives. Comparisons between deciduous and permanent results (i.e., Euclidean distances, Mantel tests, multidimensional scaling output) indicate that deciduous crown variation provides a more direct reflection of the underlying genetic structure of pedigreed samples. The morphology data are then analyzed within a quantitative genetic framework using maximum likelihood variance components analysis. Novel narrow-sense heritability and pleiotropy estimates are generated for the complete suite of deciduous and permanent crown characters, which facilitates comparisons between samples, traits, dentitions, arcades, antimeres, metameres, scoring standards, and dichotomization breakpoints. Results indicate wide-ranging but moderate heritability estimates for morphological traits, as well as low to moderate integration for characters within (deciduous-deciduous; permanent-permanent) and between (deciduous-permanent) dentitions. On average, deciduous and permanent homologues are more strongly genetically correlated than characters within the same tooth row. Results are interpreted with respect to dental development and biodistance methodology. Ultimately, the dissertation empirically validates the use of dental morphology as a proxy for underlying genetic information, including deciduous characters.
To address the paucity of deciduous-focused validation research, phenotypic distances generated from the dental data are subjected to performance analyses (biodistance simulations) and compared to genetic distances between individuals. While family-specific results vary, crown morphology performs moderately well in distinguishing relatives from non-relatives. Comparisons between deciduous and permanent results (i.e., Euclidean distances, Mantel tests, multidimensional scaling output) indicate that deciduous crown variation provides a more direct reflection of the underlying genetic structure of pedigreed samples. The morphology data are then analyzed within a quantitative genetic framework using maximum likelihood variance components analysis. Novel narrow-sense heritability and pleiotropy estimates are generated for the complete suite of deciduous and permanent crown characters, which facilitates comparisons between samples, traits, dentitions, arcades, antimeres, metameres, scoring standards, and dichotomization breakpoints. Results indicate wide-ranging but moderate heritability estimates for morphological traits, as well as low to moderate integration for characters within (deciduous-deciduous; permanent-permanent) and between (deciduous-permanent) dentitions. On average, deciduous and permanent homologues are more strongly genetically correlated than characters within the same tooth row. Results are interpreted with respect to dental development and biodistance methodology. Ultimately, the dissertation empirically validates the use of dental morphology as a proxy for underlying genetic information, including deciduous characters.
ContributorsPaul, Kathleen Siobhan (Author) / Stojanowski, Christopher M. (Thesis advisor) / Buikstra, Jane E. (Committee member) / Schwartz, Gary T. (Committee member) / Taylor, Jesse E. (Committee member) / Arizona State University (Publisher)
Created2017
Description
Early hominins present an unusual pattern of sexual dimorphism. On one hand, the canine teeth of these species are weakly size-dimorphic, vertically short, and nonhoning, suggesting a social system characterized by infrequent, low-intensity intermale competition and monogamous pair-bonding. On the other hand, marked size variation in skeletal remains attributed to species of Australopithecus is thought to reflect strong body-mass dimorphism, which is more consistent with intense intermale competition. Reconciling these conflicting signals and understanding their adaptive significance is a major goal of paleoanthropology. This dissertation research contributes to this objective by investigating factors that may constrain or reduce canine height in extant anthropoid primates. Two hypotheses regarding the relationship between canine height and other elements of the masticatory system were tested using phylogenetic comparative methods. According to the first hypothesis, canine reduction is a pleiotropic by-product of changes in the sizes of other components of the dentition. With respect to canine height, the results of this study fail to support this idea. There is limited evidence for a relationship between basal canine crown dimensions and incisor and postcanine size, but significant interspecific correlations between these variables are not strong and are restricted primarily to the female maxillary dentition. These results indicate that if pleiotropy influences canine size, then its effects are weak. The second hypothesis proposes that canine reduction is a consequence of selection for increased jaw-muscle leverage. This hypothesis receives some support: there is a clear inverse relationship between canine height and the leverage of the masseter muscle in male anthropoids. Females do not exhibit this association due to the fact that dimorphism in muscle leverage is weak or absent in most anthropoid species; in other words, female muscle leverage tracks male muscle leverage, which is linked to canine height. Leverage of the temporalis muscle is not correlated with canine height in either sex. Two specimens of the 3.0-3.7-million-year-old hominin Australopithecus afarensis fall at or beyond the upper end of the great ape range of variation in masseter leverage, which is consistent with the idea that hominin canine evolution was influenced by selection for increased jaw-muscle leverage.
ContributorsScott, Jeremiah Ezekiel (Author) / Kimbel, William H. (Thesis advisor) / Schwartz, Gary T. (Committee member) / Spencer, Mark A. (Committee member) / Arizona State University (Publisher)
Created2010