Three-rooted Mandibular First Permanent Molars in Greenland Eskimo Skulls

Abstract

The first permanent mandibular molar normally has two roots; however, in a number of individuals a third root develops. This anomaly with three roots (3RM1) occurs in between 0.9%1 and 3.4%2 of Caucasians. The anomaly is unknown in the Negro, but in Mongoloid races is of such a high prevalence as to be termed a racial characteristic. In Eskimos and Aleuts the percentage of individuals showing the anomaly has been variously reported as between 43.7% and 12.5%. The wide variation in reports based on studies of arctic peoples leads to the suspicion that the prevalence of 3RM1 may vary according to the different sub-groups of Eskimos in different geographic areas of the Arctic. Accordingly, as part of a continuing study of 3RM1 in man, a group of Eskimo skulls, all originally collected prior to 1900, were examined for the presence of this racial characteristic. ... Some 160 Eskimo skulls were identified in various museums of Great Britain. Forty of these skulls were found to be complete with mandibles and the presence of first mandibular molars or discernible tooth sockets. However, study of the museum catalogues revealed that the forty skulls originated from many parts of the North American Arctic and Greenland. Only one group, that from the west coast of Greenland, was big enough for study (29 skulls). Of the remaining specimens, 3 were from Alaska, 5 from Baffin Island, 2 from Labrador and 1 from the east coast of Greenland. ... Although the incidence of 3RM1 is given as a rate for skull, and hence individuals, the incidence as a percentage of teeth affected may be more valid. ... The determination of sex of a skull is always difficult and of doubtful reliability. ... 15 of the 29 skull were male, whilst 12 were female. The remaining two skulls were children. The sex ratio of 3RM1 was found to be 3:1 (female to male). However, with only four skulls affected, this sex ratio cannot be considered significant. ... The incidence of 12.7% by tooth count of3RM1 in this study of Greenland skulls is very close to the 12.5% reported by Pedersen from examination of skulls in Copenhagen. It would, therefore, appear that this incidence of about 12.5% was the prevailing one at the time this skull material was collected (1823-1900). However, in view of the great mixing of Caucasian genes by the introduction of Danes to Greenland, the present-day incidence of the anomaly is probably lower. Recent studies of miscegenation and 3RM1 have shown the incidence to be lower in offspring of mixed parentage. In comparison with the very high incidence of the anomaly as reported for the Aleut (43.7%) and the Alaskan Eskimo (26.7%) by Turner, the incidence in this study is closer to that for other Mongoloid races. ... Of even greater interest, however, is a comparison of this study with other reports in respect of Aleuts and Eskimos throughout the Arctic. ... there is a definite cline from west to east. The fact that this cline follows the probable migration route of the original Eskimo settlers may or may not be significant. There is an obvious need for a study on the anomaly in the Chukchi living on the Russian side of the Bering Strait. As Turner has pointed out, the 3RMI frequency variations may be explained on the basis of migrations from Asia of the three groups, Amerindian, Na-Dene and Aleut-Eskimo. He postulates a theoretical incidence of 60% in the "proto-Aleut- Eskimos". A complicating factor, which must be taken into account, particularly as regards the Greenland Eskimo, is the mixing of Caucasian genes. This commenced on the Greenland coast with the Viking settlements, and continued with the wintering over of whaling ships and fishing fleets, probably present in Davis Strait and even Baffin Bay before recorded explorations. With the continued interbreeding of the Eskimo with people of Caucasian origin, an increasingly lower incidence of the three-rooted mandibular first molar is to be expected.