The purpose of the present study was to investigate the causal relationship between walking pattern and physical malfunction using a computer simulation method with a biomechanical walking model. In this computer simulation, the musculoskeletal system was represented by a three-dimensional 14-rigid-link model and 60 muscle models. Muscular forces were controlled by a neuronal system model consisting of 16 pairs of neural oscillators. In the computational experiment, five types of walking models were constructed: an intact model, a delayed response model, a weak muscle model, an inclined posture model, and a joint contracture model. These malfunction factors were hypothesized to have a causal relationship with walking characteristics in older adults. The simulation revealed that the delayed response in the neuronal system was primarily related to walking stability. In addition, the weakening of muscles was strongly related to the reduction of the walking step length. The inclined posture and joint contracture also influenced the walking pattern, but not significantly. The use of such a computer simulation method is essential in order to clarify the causal relationship between body function and walking pattern in older adults.
The purpose of this study was to develop new standards for determining the sex of fragmentary human skeletal remains. We measured height, width, and length of the mastoid process in medieval to early modern Japanese skeletons, from the Yuigahama-minami and Hitotsubashi sites, in order to provide a metric standard for the diagnosis of sex using the mastoid process. We calculated discriminant functions based on these measurements; the accuracy of sex classification was over 80% using a single variable, and reached 82–92% with two variables, mastoid height and width. This accuracy is equal to or better than that reported by some previous studies of sex determination using the cranium. However, when we examined intra- and interobserver errors in the mastoid process measurements, we found a high level of errors, and this highlights the difficulty involved in intraobserver repeatability and interobserver reproducibility. Our results imply that, in order to achieve reliable results of sex determination using the mastoid process, the measurement methods need to be carefully determined and executed.
In an adult human skeleton of the Final Jomon age excavated at the Nakazawahama shell-mound in Iwate Prefecture, northeastern Japan, grooved enamel defects (about 2 mm in width) were observed circumferentially around the dental crowns of the upper left central incisor, upper right lateral incisor, and upper right canine. Observations of the crown surface using a stereomicroscope and evaluations of soft X-ray images revealed severe developmental defects of enamel (DDEs), having the characteristics of both enamel hypoplasia and enamel hypocalcification caused by systemic metabolic stresses. We estimated that these defects were formed at the age of late 1 year. This is the first report on such severe enamel defects in a Jomon skeleton.
The main purpose of this study was to investigate the root and canal morphology of Sri Lankan and Japanese permanent dentition. Two thousand Sri Lankan and 976 Japanese permanent teeth were examined. The number of roots in premolars and molars and the prevalence of C-shaped (gutter shaped) roots in mandibular second molars were recorded. Root canal morphology was studied using a clearing technique. The examination of root canal systems of the teeth was based on Vertucci’s classification. A higher prevalence of two-rooted maxillary first premolars was observed in Sri Lankans than in Japanese. Sri Lankan maxillary first and second premolars displayed a higher incidence of two canal and two apical foramina forms than those of Japanese. Canal morphology of mandibular first premolars showed higher occurrence of two canals with type V (1-2) canal configuration in Sri Lankans than in Japanese. In mandibular molars, Japanese presented with a higher incidence of three-rooted first molars and one-rooted second molars than Sri Lankans. C-shaped root was seen in 5.7% of Sri Lankan and 18.8% of Japanese second molars examined. In the distal root of mandibular first molars, Japanese showed a higher prevalence of two apical foramina with type IV (2) and additional canal forms than that of Sri Lankans. Japanese mandibular second molars exhibited a higher occurrence of one-root canal forms than that of Sri Lankans. In addition, mandibular incisors and canines of Sri Lankans showed a higher prevalence of two canals with type III (1-2-1) canal form than Japanese. Root and canal morphologies of Japanese and Sri Lankan people are consistent with those of people of East Asian and European (western Eurasia) origin, respectively. In human dentition, the differences of the internal canal morphology are more evident and constant than that of external root morphology among different population groups.
The excavation of the Man Bac site (c. 3800–3500 years BP) in Ninh Binh Province, Northern Vietnam, yielded a large mortuary assemblage. A total of 31 inhumations were recovered during the 2004–2005 excavation. Multivariate comparisons using cranial and dental metrics demonstrated close affinities of the Man Bac people to later early Metal Age Dong Son Vietnamese and early and modern samples from southern China including the Neolithic to Western Han period samples from the Yangtze Basin. In contrast, large morphological gaps were found between the Man Bac people, except for a single individual, and the other earlier prehistoric Vietnamese samples represented by Hoabinhian and early Neolithic Bac Son and Da But cultural contexts. These findings suggest the initial appearance of immigrants in northern Vietnam, who were biologically related to pre- or early historic population stocks in northern or eastern peripheral areas, including Southern China. The Man Bac skeletons support the ‘two-layer’ hypothesis in discussions pertaining to the population history of Southeast Asia.
Human skeletal remains from the early-modern period (17th–19th centuries AD) of Kumejima Island, the Ryukyu Islands, were examined for dental disease, including dental caries, linear enamel hypoplasia (LEH), antemortem tooth loss (AMTL), and dental calculus. The materials used in this study consisted of 386 adult individuals, 105 male, 89 female, and 192 of unknown sex. The highest rate of dental caries occurred in the adult females. Female physiological events, such as pregnancy and menopause, as well as differences in food preference may have led to this sex difference, as suggested by isotopic analysis. The high incidence of AMTL in the older females indicate that the actual rate of dental caries must have been even higher. There were no significant differences in the rate of dental caries between prehistoric foraging and early-modern farming Ryukyu Islanders, probably because of similar dietary composition of C3 plant and fish. Adult females tended to be more affected by LEH, indicating that they experienced greater physiological stress during early childhood.
The demography of the Jomon people was first systematically investigated by Kobayashi ( Journal of the Faculty of Science, The University of Tokyo, Section V, 3: 107–162). His life-table analysis indicated that Jomon life expectancy at the age of 15 was only 16 years. However, recent advances in palaeodemography have questioned whether the reconstruction of demographic parameters from skeletons actually reflects the real mortality patterns of past populations. The purpose of this study is to test the hypothesis that palaeodemographic data from skeletal remains represent an appropriate adult mortality profile. If the hypothesis is the case, the mortality profile of the Jomon people implied the heavy work-load resulting in the unusually high mortality schedule. If it is not the case, on the other hand, Kobayashi’s data had been distorted by the errors of adult age-at-death estimation. This study examined well-preserved auricular surfaces of 86 individuals, which are individuals aged 15 years and above. Age estimation of the auricular surfaces was performed using two techniques: the original method of Lovejoy et al. ( American Journal of Physical Anthropology, 68: 15–28) and the revised method of Buckberry and Chamberlain ( American Journal of Physical Anthropology, 119: 231–239). The results indicate important findings on the mortality profile of the Jomon people. First, the revised estimation has older age distributions, with the majority of individuals over 65 years of age. Second, the revised estimation increases the life expectancy at the age of 15 from 16 years to 32 years. The present data lead to the conclusions that the revised method improves the accuracy of age estimation for elderly adults, and that the Kobayashi’s estimation does not represent the real mortality profile. These findings will have great effects on the life history reconstruction of the Jomon people.
We analyzed stable carbon and nitrogen isotope ratios in a sample of human and nonhuman mammal bones excavated from the Yoshigo and Inariyama shell mounds of the Late–Final Jomon periods in Aichi Prefecture, Japan, with a view to determining individual dietary differences. To investigate possible reasons for the dietary variations identified, we related isotope ratios to sex and tooth ablation patterns. At both sites, large intra-site variations in δ13C and δ15N values were found, compared with other Jomon populations previously studied, suggesting higher than usual levels of dietary variability, and at both sites there was a positive correlation between δ13C and δ15N values. The diet of the Jomon people at both these sites had two main protein sources: marine (marine finfish and shellfish) and terrestrial (C3 plants and terrestrial mammals) protein. The intra-site variability is probably explained by consumption of these resources in different proportions. Analysis of the Yoshigo shell mound data indicated that sex is one of the factors determining dietary difference. It was also found that individual differences in diet in Yoshigo males are greater than in females. This pattern was repeated in the Inariyama shell mound data. Dietary differences were found to be related to ritual tooth ablation characteristics, particularly in males. At Inariyama, type 4I ritual tooth ablation was associated with comparatively greater dependency on terrestrial resources, while type 2C tooth ablation was associated with greater dependency on marine resources. This may indicate that type 4I males engaged predominantly in hunting, and type 2C males in fishing, as a means of food acquisition. These results are possibly the earliest evidence of occupational differentiation in the Jomon people.
Recent studies have identified a Pacific lineage (2E) of JC polyomavirus (also designated as JC virus or JCV) that occurs in both Island Southeast Asia and Oceania, but not in mainland Asia. It has been postulated that this lineage traveled with Austronesian-speaking people who are now spread throughout Island Southeast Asia and Oceania (excluding Australia and inland and southern New Guinea). However, to date, the 2E lineage has been identified in Southeast Asia only in populations of the Philippine islands. Here we report that a high incidence of the 2E lineage was detected in the people of Sumba Island, eastern Indonesia.