Associations between discontinuous cranial traits

Composition of the founding population of Iceland: biological distance and morphological variation in early historic Atlantic Europe

We examined the composition of the founding population of Iceland through the study of morphological traits in skeletons from Iceland, Ireland, Norway, and Greenland. This is the first study to address this issue from the Settlement Period of Iceland and contemporary samples from Ireland. We pose the following questions: 1) Was the founding population of Iceland of mixed or homogeneous origin? 2) Is there evidence for a significant Irish cohort in the founding population, as suggested in medieval Icelandic literature? Analysis of biodistance revealed that both Settlement Age and later samples from Iceland showed a greater degree of phenetic similarity to contemporary Viking Age Norwegians than to samples obtained from early medieval Ireland. Analysis of among-individual morphological variation showed that the Settlement Age population of Iceland did not exhibit an increase in variation in comparison to other populations in the sample, suggesting a relatively homogenous origin. However, estimation of admixture between the Irish and Norwegian populations indicated that 66% of the Icelandic settlers were of Norwegian origin. Comparison of the Icelandic samples to hybrid samples produced by resampling the Viking Age Norwegian and early medieval Irish samples revealed that the Icelandic samples are much closer to the Norwegian samples than expected, based on a 66:34 mixture of Norwegian and Irish settlers. We conclude that the Settlement Age population of Iceland was predominantly (60-90%) of Norwegian origin. Although this population was relatively homogenous, our results do not preclude significant contributions from Ireland as well as other sources not represented in our analysis.

Characterization of biological diversity through analysis of discrete cranial traits

In the present study, the frequency distributions of 20 discrete cranial traits in 70 major human populations from around the world were analyzed. The principal-coordinate and neighbor-joining analyses of Smith's mean measure of divergence (MMD), based on trait frequencies, indicate that 1). the clustering pattern is similar to those based on classic genetic markers, DNA polymorphisms, and craniometrics; 2). significant interregional separation and intraregional diversity are present in Subsaharan Africans; 3). clinal relationships exist among regional groups; 4). intraregional discontinuity exists in some populations inhabiting peripheral or isolated areas. For example, the Ainu are the most distinct outliers of the East Asian populations. These patterns suggest that founder effects, genetic drift, isolation, and population structure are the primary causes of regional variation in discrete cranial traits. Our results are compatible with a single origin for modern humans as well as the multiregional model, similar to the results of Relethford and Harpending ([1994] Am. J. Phys. Anthropol. 95:249-270). The results presented here provide additional measures of the morphological variation and diversification of modern human populations.

Frequency variations of discrete cranial traits in major human populations. III. Hyperostotic variations

Seven discrete cranial traits usually categorised as hyperostotic characters, the medial palatine canal, hypoglossal canal bridging, precondylar tubercle, condylus tertius, jugular foramen bridging, auditory exostosis, and mylohyoid bridging were investigated in 81 major human population samples from around the world. Significant asymmetric occurrences of the bilateral traits were detected in the medial palatine canal and jugular foramen bridging in several samples. Significant intertrait associations were found between some pairs of the traits, but not consistently across the large geographical samples. The auditory exostosis showed a predominant occurrence in males. With the exception of the auditory exostosis and mylohyoid bridging in a few samples, significant sex differences were slight. The frequency distributions of the traits (except for the auditory exostosis) showed some interregional clinality and intraregional discontinuity, suggesting that genetic drift could have contributed to the observed pattern of variation.

Frequency variations of discrete cranial traits in major human populations. II. Hypostotic variations

Five discrete hypostotic cranial traits, tympanic dehiscence, ovale-spinosum confluence, metopism, transverse zygomatic suture vestige, and biasterionic suture, were investigated in 81 human population samples. Except for ovale-spinosum confluence, marked asymmetric occurrences of the bilateral traits were not detected in the majority of the samples. Significant intertrait association was observed mainly between the biasterionic suture and other sutural variations including accessory ossicles. The traits showing relatively consistent sex differences across diverse populations were tympanic dehiscence, which is predominant in females, and biasterionic suture in males. On a world scale, the 5 hypostotic cranial traits showed distinctive patterns of geographical variation. Different clinal variations within and between macrogeographical areas such as western and eastern parts of the Old World were found for the frequencies of the traits. The Ainu may be the most distinct outlier in the eastern Asian region on the basis of the incidence of the traits, especially the transverse zygomatic suture vestige. The interregional variation without reasonable adaptive value and nonadaptive shift of the possible outliers presented in this study suggest that the genetic background for the occurrence of these traits cannot be excluded completely.

Frequency variations of discrete cranial traits in major human populations. I. Supernumerary ossicle variations

Four supernumerary ossicle variations-the ossicle at the lambda, the parietal notch bone, the asterionic bone, and the occipitomastoid bone-were examined for laterality differences, intertrait correlations, sex differences, and between group variations in the samples from around the world. Significant laterality differences were not detected in almost all samples. In some pairs of traits, significant association of occurrence were found. Several geographic samples were sexually dimorphic with respect to the asterionic bone and to a lesser extent for the parietal notch bone. East/Northeast Asians including the Arctic populations in general had lower frequencies of the 4 accessory ossicles. Australians, Melanesians and the majority of the New World peoples, on the other hand, generally had high frequencies. In the western hemisphere of the Old World, Subsaharan Africans had relatively high frequencies. Except for the ossicle at the lambda, the distribution pattern in incidence showed clinal variation from south to north. Any identifiable adaptive value related to environmental or subsistence factors may be expressed in such clinal variation. This may allow us to hypothesise that not only mechanical factors but a founder effect, genetic drift, and population structure could have been the underlying causes for interregional variation and possible clines in the incidences of the accessory ossicles.

Quantitative genetics of skeletal nonmetric traits in the rhesus macaques on Cayo Santiago. II. Phenotypic, genetic, and environmental correlations between traits

The general lack of phenotypic correlation among skeletal nonmetric traits has been interpreted as indicating a lack of genetic correlation among these traits. Nonmetric traits scored on animals in the skeletal collection of rhesus macaques from Cayo Santiago are used to calculate phenotypic, genetic, and environmental correlations between traits. The results show that even when phenotypic correlations are low, there may be large, significant genetic correlations among these traits. The genetic correlation pattern suggests that genes which affect nonmetric trait variation act primarily at a local level in the cranium, even though there are genes with pleiotropic effects on skeletal nonmetric traits throughout the cranium. Environmental and phenotypic correlations do not show this neighborhood pattern of correlation.

Bilateral asymmetry of human skeletal non-metric traits

The use of non-metric skeletal traits to compute population distance statistics assumes strong genetic control of trait expression. An investigation of bilateral asymmetry frequencies of human cranial and postcranial non-metric traits shows that asymmetry is common. This suggests that environmental stress, as well as the genotype, is important in controlling trait frequencies.

Within and between race distances in population studies based on discrete traits of the human skull

A battery of 24 discrete cranial traits has been tested for its power to discriminate within- and between-race distances for the two principal North American indigenous populations: Indian (7 samples, N = 366) and Eskimo (7 samples, N = 451). One of the Indian samples, Dakota Sioux, has been split according to tribal subdivisions, the intra-tribal mean distance providing a parameter of very close relationship. In addition, two Negro samples provide a parameter of relationship phylogenetically remote from the Amerinds. Separate male-female analysis of the three largest samples indicates that distances for pooled samples are not seriously affected by the sex component. Within-race distances (C. A. B. Smith's Measure of Divergence, MD), are smaller than between-race at the .00001 level of significance (Mann-Whitney U test) for both Indian-Eskimo and Amerind-Negro comparisons. The features most powerful for Indian-Eskimo and Amerind-Negro comparisons. The features most powerful for Indian-Eskimo discrimination are revealed by their percent contribution to the mean of 49 MD's. The African heritage of American Blacks is reflected in a characteristic Negro pattern of trait frequencies different from the Amerind. This battery of features yields valid taxonomical information useful in conjunction with other physical data to reconstruct affinities of extinct populations.