Diachronic changes in craniofacial morphology among the middle-late Holocene populations from Hehuang region, Northwest China.

OBJECTIVES: This study analyzes craniofacial shape variation in the Hehuang region of Northwest China within a population genetic framework, and takes a diachronic approach to explore the relationship betwee cultural discontinuity and biological continuity/discontinuity in the Hehuang region during the middle to late Holocene. MATERIALS AND METHODS: The sample comprises 76 adult skulls from five archaeological sites, ranging from 4,500 to 1,530 BP. 3D geometric morphometrics, multivariate statistics, quantitative evolutionary genetic and biodistance analyses were performed to study the diachronic variation in craniofacial morphology. Analyses were performed on two cranial modules: the face and the cranial vault, across three major diachronic groups representing the late Neolithic (LNA), the Bronze Age (BA), and the Han-Jin dynasty (HD). RESULTS: Average regional FST for both cranial modules was low, indicating relatively greater variation within diachronic groups than among them. While the LNA and BA groups did not show any significant differences in facial and vault shape, significant craniofacial shape changes were detected between the BA and HD groups. DISCUSSION: The consistent craniofacial morphology during the LNA and the BA, and the shift in morphology between the BA and the HD indicates that cultural discontinuity does not always coincide with biological discontinuity. The Hehuang population evolved in situ with few changes, despite cultural and dietary changes, until the HD when migrations from the Central Plains are associated with extra-local gene flow to the area.

Plasticity and constraint in response to early-life stressors among late/final Jomon period foragers from Japan: evidence for life history trade-offs from incremental microstructures of enamel.

This study evaluates two hypotheses that address how Late/Final Jomon period people responded to early-life stress using linear enamel hypoplasia (LEH) and incremental microstructures of enamel. The first hypothesis predicts that Jomon people who experienced early-life stressors had greater physiological competence in responding to future stress events (predictive adaptive response). The second hypothesis predicts that Jomon people traded-off in future growth and maintenance when early investment in growth and survival was required (plasticity/constraint). High resolution tooth impressions were collected from intact, anterior teeth and studied under an engineer's measuring microscope. LEH were identified based on accentuated perikymata and depressions in the enamel surface profile. Age of formation for each LEH was estimated by summing counts of perikymata and constants associated with crown initiation and cuspal enamel formation times. The relationship between age-at-first-defect formation, number of LEH, periodicity between LEH, and mortality was evaluated using multiple regression and hazards analysis. A significant, positive relationship was found between age-at-death relative to age-at-first-defect formation and a significant, negative relationship was found between number of LEH relative to age-at-first-defect formation. Individuals with earlier forming defects were at a significantly greater risk of forming defects at later stages of development and dying at younger ages. These results suggest that Late/Final Jomon period foragers responded to early-life stressors in a manner consistent with the plasticity/constraint hypothesis of human life history. Late/Final Jomon period individuals were able to survive early-life stressors, but this investment weakened responses to future stress events and exacerbated mortality schedules.

A comparative study of stress episode prevalence and duration among Jomon period foragers from Hokkaido.

This study reconstructs linear enamel hypoplasia (LEH) prevalence and stress episode duration among Jomon period foragers from Hokkaido, Japan (HKJ). Results are compared to Jomon period samples from coastal Honshu, Japan (HSJ) and Tigara Inupiat from Point Hope, Alaska (PHT) to provide a more comprehensive perspective on the manifestation of stress among circum-Pacific foragers. LEH were identified macro- and microscopically by enamel surface depressions and increased perikymata spacing within defects. Individuals with more than one anterior tooth affected by LEH were labeled as LEH positive. Stress episode durations were estimated by counting the number of perikymata within the occlusal wall of each LEH and multiplying that number by constants reflecting modal periodicities for modern human teeth. LEH prevalence and stress episode duration did not differ significantly between the two Jomon samples. Significantly greater frequencies of LEH were found in HKJ as compared to PHT foragers. However, HKJ foragers had significantly shorter stress episode durations as compared to PHT. This suggests that a greater proportion of HKJ individuals experienced stress episodes than did PHT individuals, but these stress events ended sooner. Similarity in stress experiences between the two Jomon samples and differences between the HKJ and PHT are found. These findings are important for two reasons. First, stress experiences of foraging populations differ markedly and cannot be generalized by subsistence strategy alone. Second, due to significant differences in episode duration, stress experiences cannot be understood using prevalence comparisons alone.

Ontogeny of limb proportions in late through final Jomon period foragers.

This study reports on developmental patterning in the intralimb indices of Late/Final Jomon period (4000-2300 BP) people. Jomon foragers represent the descendants of migrants from Northeast Asia, who arrived in the Japanese Islands around 20,000 BP. Among adults, Jomon brachial indices are elevated and similar to warm adapted, low latitude people, while crural indices are intermediate and similar to people from moderate latitudes. Two hypotheses regarding the development of intralimb indices among Jomon period foragers are tested: (1) intralimb indices of Jomon people maintain predicted ecogeographic relationships over ontogeny; (2) greater evolvability will be observed in the brachial index, while greater developmental constraint will be observed in the crural index. Changes in intralimb proportions in a Jomon skeletal growth series are compared to those in two contrasting samples: Inuit from Point Hope (cold adapted) and Nubians from Kulubnarti (warm adapted). A quadratic equation best describes the ontogeny of brachial and crural indices, with high indices in infancy followed by a decline in childhood and an increase in adolescence. Despite these shifts, ecogeographically predicted differences and similarities in the indices are maintained between samples throughout ontogeny. In addition, radial relative to humeral length is significantly less correlated than tibial relative to femoral length. These results suggest genetic conservation of intralimb indices over the course of development. However, radial and humeral lengths are less correlated than tibial and femoral lengths among Jomon subadults and adults, potentially suggesting greater evolvability of the brachial index and more developmental constraint on the crural index.

Variability in dental caries prevalence between male and female foragers from the Late/Final Jomon period: Implications for dietary behavior and reproductive ecology.

OBJECTIVES: This study documents sex differences in dental caries prevalence among Late to Final Jomon period (4000 through 2300 BP) foragers from Japan and interprets the results within behavioral, dietary, and reproductive context. METHODS: The presence/absence of carious lesions was recorded from ∼1600 Late/Final Jomon period teeth. Frequencies and mean numbers of carious teeth were compared between males and females according to age, tooth group, and region using Fisher's exact and t tests. RESULTS: Significantly greater frequencies of carious molar teeth were observed in females compared to males in each age group. Few differences were observed between older and younger females as well as between females from high and low density regions. Significantly greater prevalence of cariogenic molars were, however, observed between females in Age Group 3 from a high compared to low density region. Significantly greater average numbers of carious molar teeth were found in females compared to males, with no significant differences in mean number of carious teeth between age groups. CONCLUSIONS: Differences in carious teeth between the sexes likely reflect behavioral and dietary variation for males and females. Limited differences in caries prevalence and mean number of carious teeth between female age groups and regions of varying population density suggests that reproductive factors played a minor role in dental caries variation between males and females.

Patterns of systemic stress during the agricultural transition in prehistoric Japan.

This study documents and interprets systemic stress during the agricultural transition in prehistoric Japan using linear enamel hypoplasia (LEH) defects and cribra orbitalia (CO) lesions. Middle to Final Jomon cultures (5000-2300 BP) from Honshu Island represent the foraging samples, while Yayoi cultures (2500-1700 BP) represent the early agricultural samples. Jomon foragers from eastern Japan had broad-based, intensive economies. Jomon foragers from western Japan had a greater focus on seasonally available, nutritionally poor resources, while Yayoi people were descendents of migrants from the East Asian continent and introduced wet rice economies to Japan. This study tests the hypotheses that wet rice economies will be associated with a lower prevalence of teeth/individuals affected by LEH defects in western Japan, while few differences in the prevalence of teeth/individuals with LEH defects will be observed between eastern Jomon people and Yayoi farmers. It is further predicted that similar CO prevalence will be observed between Jomon and Yayoi people given environmental similarities. Significantly greater frequencies of teeth affected by LEH defects are observed among western Jomon compared to Yayoi people. The prevalence of teeth with LEH defects is slightly elevated among eastern Jomon foragers compared to Yayoi agriculturalists. Significant differences in CO prevalence are not observed. Systemic stress prevalence in western Japan likely declined following wet-rice agriculture because this crop provided a predictable, renewable resource base. Systemic stress prevalence was similar between eastern Jomon and Yayoi people because both groups practiced intensive subsistence strategies. Similar CO prevalence reflects infectious diseases associated with living conditions.

Variation in limb proportions between Jomon foragers and Yayoi agriculturalists from prehistoric Japan.

Variation in limb proportions between prehistoric Jomon and Yayoi people of Japan are explored by this study. Jomon people were the descendents of Pleistocene nomads who migrated to the Japanese Islands around 30,000 yBP. Phenotypic and genotypic evidence indicates that Yayoi people were recent migrants to Japan from continental Northeast Asia who likely interbred with Jomon foragers. Limb proportions of Jomon and Yayoi people were compared using RMA regression and "Quick-Test" calculations to investigate relative variability between these two groups. Cluster and principal components analyses were performed on size-standardized limb lengths and used to compare Jomon and Yayoi people with other groups from various climatic zones. Elongated distal relative to proximal limb lengths were observed among Jomon compared to Yayoi people. Jomon limb proportions were similar to human groups from temperate/tropical climates at lower latitudes, while Yayoi limb proportions more closely resemble groups from colder climates at higher latitudes. Limb proportional similarities with groups from warmer environments among Jomon foragers likely reflect morphological changes following Pleistocene colonization of the Japanese Islands. Cold-derived limb proportions among the Yayoi people likely indicate retention of these traits following comparatively recent migrations to the Japanese Islands. Changes in limb proportions experienced by Jomon foragers and retention of cold-derived limb proportions among Yayoi people conform to previous findings that report changes in these proportions following long-standing evolution in a specific environment.

Dental caries prevalence as evidence for agriculture and subsistence variation during the Yayoi period in prehistoric Japan: biocultural interpretations of an economy in transition.

The Yayoi period represents the earliest point of agricultural dependence in Japan, dating from approximately 2500 BP to AD 300. Yayoi period people consumed wet-rice as a primary subsistence base. This article uses dental caries prevalence to interpret the biocultural implications of agriculture among these people by testing the following hypotheses: 1) Yayoi period agriculturalists had greater frequencies of carious teeth than Jomon period foragers, 2) regional variation in carious tooth frequencies will be observed among Yayoi period agriculturalists, while 3) variation in carious tooth frequencies will be observed between male and female agriculturalists. Statistically significant differences in carious teeth were observed between the agriculturalists from Southern Honshu and all other samples. These differences suggest greater reliance on cariogenic plants among farmers from Southern Honshu and are consistent with an agricultural economy. The people of the Yayoi period from Tanegashima Island and Northern Kyushu did not have significantly different carious tooth frequencies compared to Jomon period foragers. This suggests that rice alone was not a more cariogenic dietary substance than those consumed by Jomon period foragers but a cariogenic food nonetheless. Dietary heterogeneity between the prehistoric people of the Yayoi period from Southern Honshu and those from Northern Kyushu and Tanegashima Island is also inferred from these differences. Significantly greater frequencies of carious teeth among older aged Yayoi period females compared with males suggest dietary differences between the sexes.

Dietary variation and stress among prehistoric Jomon foragers from Japan.

Current archaeological evidence indicates that greater dietary reliance on marine resources is recorded among the eastern Jomon, while plant dependence prevailed in western/inland Japan. The hypothesis that the dietary choices of the western/inland Jomon will be associated with greater systemic stress is tested by comparing carious tooth and enamel hypoplasia frequencies between the eastern and western/inland Jomon. Demographic collapse coincides with climate change during the Middle to Late Jomon period, suggesting dwindling resource availability. It is hypothesized that this change was associated with greater systemic stress and/or dietary change among the Middle to Late Jomon. This hypothesis is tested by comparing enamel hypoplasia and carious tooth frequencies between Middle to Late and Late to Final Jomon foragers. Enamel hypoplasia was significantly more prevalent among the western/inland Jomon. Such findings are consistent with archaeological studies that argue for greater plant consumption and stresses associated with seasonal resource depletion among the western/inland Jomon. Approximately equivalent enamel hypoplasia frequencies between Middle to Late and Late to Final Jomon foragers argues against a demographic collapse in association with diminished nutritional returns. Significant differences in carious tooth frequencies are, however, observed between Middle to Late and Late to Final Jomon foragers. These results suggest a subsistence shift during the Middle to Late Jomon period, perhaps in response to a changed climate. The overall patterns of stress documented by this study indicate wide-spread environmentally directed biological variation among the prehistoric Jomon.