BackgroundThe patterning cascade model of tooth morphogenesis accounts for shape development through the interaction of a small number of genes. In the model, gene expression both directs development and is controlled by the shape of developing teeth. Enamel knots (zones of nonproliferating epithelium) mark the future sites of cusps. In order to form, a new enamel knot must escape the inhibitory fields surrounding other enamel knots before crown components become spatially fixed as morphogenesis ceases. Because cusp location on a fully formed tooth reflects enamel knot placement and tooth size is limited by the cessation of morphogenesis, the model predicts that cusp expression varies with intercusp spacing relative to tooth size. Although previous studies in humans have supported the model's implications, here we directly test the model's predictions for the expression, size, and symmetry of Carabelli cusp, a variation present in many human populations.Methodology/Principal FindingsIn a dental cast sample of upper first molars (M1s) (187 rights, 189 lefts, and 185 antimeric pairs), we measured tooth area and intercusp distances with a Hirox digital microscope. We assessed Carabelli expression quantitatively as an area in a subsample and qualitatively using two typological schemes in the full sample. As predicted, low relative intercusp distance is associated with Carabelli expression in both right and left samples using either qualitative or quantitative measures. Furthermore, asymmetry in Carabelli area is associated with asymmetry in relative intercusp spacing.Conclusions/SignificanceThese findings support the model's predictions for Carabelli cusp expression both across and within individuals. By comparing right-left pairs of the same individual, our data show that small variations in developmental timing or spacing of enamel knots can influence cusp pattern independently of genotype. Our findings suggest that during evolution new cusps may first appear as a result of small changes in the spacing of enamel knots relative to crown size.

Previous researchers hypothesized that tooth types forming during early childhood should be less sexually dimorphic than those forming during later childhood, if sex hormone concentration differences between males and females increase progressively throughout childhood and can affect tooth size. Descriptive tooth size data have recently been cited in support of this hypothesis, particularly with respect to differences in sexual dimorphism among the tooth types of tooth classes. The present study tests this hypothesis for the mesiodistal dimension of human permanent teeth using published data for incisor, premolar, and molar tooth classes from seven diverse populations. The sample size for each tooth type per population was at least 50. This study also tests a modification of this hypothesis which takes into account the postnatal testosterone surge in males and the low levels of sex hormones in both sexes prior to puberty. Predictions are developed for both the original and modified hypotheses. The "D" statistic, the total area of nonoverlap between the phenotypic distributions of males and females, is used to quantify sexual dimorphism. Comparison of D values for different tooth types within tooth classes across these seven populations does not strongly support either hypothesis. These results suggest that gross changes in sex hormone concentrations during development are not related to population-wide patterns of sexual dimorphism among the tooth types of human permanent tooth classes, as recent studies indicate. This finding is consistent with other studies which suggest that sex hormones have only a minor role in generating crown size sexual dimorphism.

Traumatic injuries can be used as general indicators of activity patterns in past populations. This study tests the hypothesis that contemporaneous (10th–12th century) rural and urban populations in medieval Poland will have a significantly different prevalence of non-violent fractures. Traumatic injuries to the post-cranial skeleton were recorded for 180 adults from rural Giecz and for 96 adults from urban Poznań-Śródka. They were statistically analyzed by body region and individual skeletal element. Results reveal that Giecz had a significantly higher rate of trunk fractures than Poznań-Śródka (Fisher’s exact, p<0.05). In particular, rib and vertebral fractures were more common in Giecz males and females than in their Poznań-Śródka counterparts. Traumatic injuries in the extremities were comparable between the two samples, suggesting similar risks of trauma to these regions. These results indicate that in early medieval Poland, activities associated with a rural lifestyle resulted in more injuries. These stress or accidental fractures, which are related to a high-risk setting, were not consistent with an urban lifestyle. Overall, agricultural populations like Giecz were engaged in a laborious lifestyle, reflected in a variety of injuries related to repetitive, high-risk activities. Although urban populations like Poznań engaged in craft specialization participated in repetitive activities, their lifestyle resulted in lesser fracture-risk.

Apotropaic observances-traditional practices intended to prevent evil-were not uncommon in post-medieval Poland, and included specific treatment of the dead for those considered at risk for becoming vampires. Excavations at the Drawsko 1 cemetery (17th–18th c. AD) have revealed multiple examples (n = 6) of such deviant burials amidst hundreds of normative interments. While historic records describe the many potential reasons why some were more susceptible to vampirism than others, no study has attempted to discern differences in social identity between individuals within standard and deviant burials using biogeochemical analyses of human skeletal remains. The hypothesis that the individuals selected for apotropaic burial rites were non-local immigrants whose geographic origins differed from the local community was tested using radiogenic strontium isotope ratios from archaeological dental enamel. 87Sr/86Sr ratios ( = 0.7112±0.0006, 1σ) from the permanent molars of 60 individuals reflect a predominantly local population, with all individuals interred as potential vampires exhibiting local strontium isotope ratios. These data indicate that those targeted for apotropaic practices were not migrants to the region, but instead, represented local individuals whose social identity or manner of death marked them with suspicion in some other way. Cholera epidemics that swept across much of Eastern Europe during the 17th century may provide one alternate explanation as to the reason behind these apotropaic mortuary customs, as the first person to die from an infectious disease outbreak was presumed more likely to return from the dead as a vampire.

Treponemal disease is known to be associated with the compromised community health of permanent village settlement. This association explains its high visibility in the village-based, arguably chiefdom level, agriculturalist societies of late prehistoric (AD 1300-1600) North America. Within chiefdom-level societies, health differences have often been demonstrated between mortuary-defined "elite" and "nonelite" individuals. This theoretically should predict status-based differences in treponemal disease visibility. The prediction is tested in a five-site osteological sample (N = 650) from the Dallas phase (AD 1300-1550), a simple mortuary-defined two-tiered presumptive chiefdom level maize agriculturalist socioeconomic context from lower east Tennessee. The Dallas phase results affirm a general pre-Colombian North American pattern of no sex differences and display comparable adult to subadult frequencies. The study also reveals that given a sufficient sample size, "elites" do indeed exhibit a significantly lower frequency of tertiary stage treponemal disease. This can be attributed to better baseline health, which has been previously demonstrated in this sample. It may also be affected by the mortuary inclusion of achieved status individuals whose good health may have facilitated sociopolitical advancement. Another pattern that emerged is an apparent young adult age bias in disease visibility. This suggests that tertiary treponemal disease morbidity may either directly or synergistically factor in early adult age at death. Future research will address the veracity of this association.