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Adrift in Oceania: The Roles of Genetic Drift and Natural Selection In Explaining the Unusual Dental Pattern of New Guinea Highlanders
AdvisorScott, G. Richard
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A primary goal was to resolve the ‘baffling convergence’ of New Guinea and European dental morphology. This is an unusual case where dental morphology is at odds with other lines of biological evidence that show close ties between New Guinea and Australian populations. Observations were made on 182 dental casts from living populations in the New Guinea Highlands to characterize their dental morphology. Trait frequencies were compared to those of world populations to compute distance statistics and derive dendrograms. The conundrum was solved to a large extent when variation of the EDAR gene variant 370A was taken into account. This gene is associated with multiple traits involving hair, skin, and teeth. The high frequency of this polymorphism in North Asia is associated with a high frequency of shovel-shaped incisors. The EDAR 370A gene is not only associated with shoveling but also with double shoveling and lower molar cusp number. Although the gene is in moderate to high frequencies throughout Asia and the Pacific, it is absent in New Guinea. When the dental traits associated with EDAR were removed from the distance analysis, New Guinea now linked with Australia and Melanesia rather than Europe. This suggests that the unusual dental pattern exhibited by New Guinea Highlanders is a product of both genetic drift and natural selection. When compared to other populations, non-EDAR linked traits exhibit distance values that are in accord with differentiation attributable to genetic drift. The EDAR-linked traits reflect selection that has driven the frequency of this gene to zero. In all likelihood, the dental traits associated with EDAR are ‘genetic hitchhikers’ associated with some skin and/or hair trait that have been influenced by selection in this tropical rainforest environment. Although the nature of this selection cannot be determined, at least the ‘baffling convergence’ of New Guinean and European tooth crown morphology has been ‘unbaffled.’