Frequency and variation of three-rooted lower first permanent molars in precontact Easter Islanders and in Pre-Conquest Peruvians

Abstract

The purpose of this study was to evaluate the prevalence of mandibular first molars featuring a distolingual root in two archeological collections. A total of 172 teeth from Pre-Contact Easter Islanders and 281 teeth from three Pre-Conquest Peruvian sites were examined looking for the presence of three-rooted lower first permanent molars (3RLM1). The Easter Island teeth were recovered during the Ahu Tongariki excavation Project 1993-2001: we identified 70 M1s, 62 M2s and 40 M3s. The sample contained 20 lower molars with an extra root, meaning that there is 29% with 3RLM1. The Peruvian teeth are from three archeological sites: Nasca (Proyecto Nasca, n = 100), Arequipa (Proyecto Condesuyos, n = 28), and Tablada de Lurín (Proyecto Loma de Lesix, n = 153). We found 8% of 3RLM1 at Nasca, 1.2% at Tablada de Lurín, and 9% at Condesuyos (total frequency = 6%). The percentage of 3RLM1 in Easter Island, very high compared to the whole Polynesia and the Peruvian sample, shows the effect of a genetic bottleneck (accidental reduction of a population), which the settlers went through as they reached the island they named Rapa Nui. We conclude that founder effect and genetic drift have played an important role in regulating the past and present mosaic distribution of 3RLM1 in insular populations.