Three‐rooted mandibular first permanent molars and the question of American Indian Origins

Three‐rooted mandibular first molars (3RM1) are characteristic of Asian and Asian‐derived populations, particularly Aleuts (whose 3RM1 frequency is the highest in the world) and Eskimos. Similarities in the frequency of these teeth between American Indians and contemporary peoples of southeastern Asia indicate a closer relation between these groups than between American Indians and Aleut‐Eskimos. Three‐rooted mandibular first molar frequency does not differ significantly in males and females except in Aleut‐Eskimos. Bilateral asymmetry of 3RM1 is relatively frequent in both sexes and all groups. All American Indian groups examined have a low frequency of 3RM1 pointing to a single Asian origin, except Athabaskan‐speaking Arizona Navajos, whose 3RM1 frequency approaches that of Aleut‐Eskimos. There is no evidence at present of any significant local microevolution of 3RM1 in two testable prehistoric American Indian groups, although genetic drift had possibly occurred in a few series of 3RM1‐deficient southwestern U. S. prehistoric Western Pueblo Indians. No adaptive value can be found for 3RM1 in Indians. In prehistoric western U. S. Indians geographic frequency variation is only slightly greater than the very slight (and non‐significant) testable temporal variation. Three migrations from Asia seem best to explain New World 3RM1 frequency variation.