Linear enamel hypoplasias as indicators of systemic physiological stress: evidence from two known age-at-death and sex populations from postmedieval London

Enamel hypoplasias are useful indicators of systemic growth disturbances during childhood, and are routinely used to investigate patterns of morbidity and mortality in past populations. This study examined the pattern of linear enamel hypoplasias in two different burial populations from 18th and 19th Century church crypts in London. Linear enamel hypoplasias on the permanent dentitions of individuals from the crypt of Christ Church, Spitalfields, were compared to enamel defects on the teeth of individuals from St. Bride's. The method used involves the identification of enamel defects at a microscopic level, and systemic perturbations are detected by matching hypoplasias among different tooth classes within each individual. The pattern of linear enamel hypoplasias was contrasted between individuals from the burial sites of Spitalfields and St. Bride's, between males and females, and between those aged less than 20 years of age and those aged over 20 years at death. Six different parameters were examined: frequency of linear enamel hypoplasias, interval between defects, duration of hypoplasias, age at first occurrence of hypoplasia, age at last occurrence of hypoplasia, and the percentage of enamel formation time taken up by growth disturbances. All individuals in the study displayed linear enamel hypoplasias, with up to 33% of total visible enamel formation time affected by growth disruptions. Multiple regression analysis indicated a number of significant differences in the pattern of enamel hypoplasias. Individuals from Spitalfields had shorter intervals between defects and greater percentages of enamel formation time affected by growth disturbances than did individuals from St. Bride's. Females had greater numbers of linear enamel hypoplasias, shorter intervals between defects, and greater percentages of enamel formation time affected by growth disturbances than males. There were also differences in the pattern of enamel hypoplasias and age at death in this study. Individuals who died younger in life had an earlier age at first occurrence of enamel hypoplasia than those who survived to an older age. The pattern of enamel hypoplasias detected in this study was influenced by tooth crown geometry and tooth wear such that most defects were found in the midcrown and cervical regions of the teeth, and greater numbers of defects were identified on the anterior teeth. Differences in sensitivity of the parameters used for the detection of enamel hypoplasias were found in this study. The percentage of visible enamel formation time affected by growth disturbances was the parameter that identified the greatest number of significant differences among the subgroups examined.     

Frequency and distribution of enamel hypoplasias in a historic skeletal sample

A skeletal sample of 296 individuals from a 19th century American poorhouse cemetery is examined for the frequency and chronological distribution of linear enamel hypoplasias on the mandibular canines and maxillary central incisors. Dental enamel hypoplasias may be considered to be indicators of increased exposure to health risk at the time of weaning. The purpose of this study is to examine childhood stress and provide a relative measure of that stress, as evidenced by hypoplasias, in a historic sample that represents an industrializing population. The frequency of enamel hypoplasias per individual by tooth ranged from 70 to 73%, with a peak age at stress of 2.5 to 3 years for the maxillary central incisor and 3.5 to 4 years for the mandibular canine. There were no significant differences in the presence of hypoplasias between males and females. The peak age at stress between 2.5 and 4 years in this 19th century sample transects the ranges reported for prehistoric populations (2-6 years) and for modern groups (0-3 years). These results indicate that the stress associated with weaning probably occurred earlier in incipient industrial societies than in prehistoric hunter/gatherers and agriculturalists, yet not as early as in modern industrial groups. The high level of childhood stress in this skeletal sample compared with that of other samples may indicate a change in health, at least among the lowest class, associated with the cultural transition from an agricultural to an industrial society.     

Reevaluating Harris lines--a comparison between Harris lines and enamel hypoplasia

This study examines the association between Harris lines and enamel hypoplasia. This association is analyzed in terms of: 1) presence/absence of these markers in each individual, and 2) age of the individuals at the time of Harris lines and enamel hypoplasias formation. Data from two archaeological groups (Azapa-71 and Azapa-140) from northern Chile were analyzed. The results indicate Harris lines and enamel hypoplasias are not associated in terms of presence/absence. Moreover, the estimated age of the individuals at the time of Harris lines and enamel hypoplasia formation shows that these two markers have a very different distribution. While enamel hypoplasias clustered between ages 3 and 5, Harris lines were more commonly formed during the first year of life, as well as during adolescence, which are the periods of most accelerated growth. We propose that Harris lines are a result of a normal, rather than abnormal, saltatory growth process.     

Stress physiologique et état de santé des plus anciens Hommes anatomiquement modernes du sud-est de l’Europe (données dentaires,couche 6-1, Buran-Kaya III,Crimée)

Buran-Kaya III site, in Crimea, provides an exceptional stratigraphic sequence, extending from Middle Paleolithic to Neolithic. Among the archaeological layers allocated to the Gravettian (sensu lato), more than 170 anthropological remains have been discovered in the layer 6-1. They represent the oldest Upper Paleolithic modern humans from Eastern Europe in a well-documented archaeological context. The aim of this article, based on dental remains and enamel dental hypoplasias in particular, is to evaluate the health of the modern humans, which lived more than 32,000 years BP ago in Crimea. This study puts into the light the low frequency of hypoplasias (occurring in the two youngest individuals). This article complete the rare studies concerning the presence of this physiological stress during the Early Upper Paleolithic and confirm the scarcity of enamel dental hypoplasias and dental pathologies, such as caries, at this period.     

Enamel hypoplasia in the Middle Pleistocene hominids from Atapuerca (Spain)

The prevalence and chronology of enamel hypoplasias were studied in a hominid dental sample from the Sima de los Huesos (SH) Middle Pleistocene site at the Sierra de Atapuerca (Burgos, northern Spain). A total of 89 permanent maxillary teeth, 143 permanent mandibular teeth, and one deciduous lower canine, belonging to a minimum of 29 individuals, were examined. Excluding the antimeres (16 maxillary and 37 mandibular cases) from the sample, the prevalence of hypoplasias in the permanent dentition is 12.8% (23/179), whereas the deciduous tooth also showed an enamel defect. No statistically significant differences were found between both arcades and between the anterior and postcanine teeth for the prevalence of hypoplasias. In both the maxilla and the mandible the highest frequency of enamel hypoplasias was recorded in the canines. Only one tooth (a permanent upper canine) showed two different enamel defects, and most of the hypoplasias were expressed as faint linear horizontal defects. Taking into account the limitations that the incompleteness of virtually all permanent dentitions imposes, we have estimated that the frequency by individual in the SH hominid sample was not greater than 40%. Most of the hypoplasias occurred between birth and 7 years (N = 18, X = 3.5, SD = 1.3). Both the prevalence and severity of the hypoplasias of the SH hominid sample are significantly less than those of a large Neandertal sample. Furthermore, prehistoric hunter-gatherers and historic agricultural and industrial populations exhibit a prevalence of hypoplasias generally higher than that of the SH hominids. Implications for the survival strategies and life quality of the SH hominids are also discussed. © 1995 Wiley-Liss, Inc.     

Response of bone and enamel formation to nutritional supplementation and morbidity among malnourished Guatemalan children

The effects of changes in nutritional and health status upon bone and enamel development are examined in a sample of 63 rural Guatemalan children (24 females, 39 males). The number of ossified hand-wrist centers at 3 years and the number of linear enamel hypoplasias (LEH) in ～0–3 year zones of developing teeth were used to monitor the response of bone mineralization and enamel matrix formation to illness and nutritional supplementation. Numbers of ossified centers and LEH were compared across sex, supplementation, and morbidity groups. Enamel matrix secretion responded positively to increased supplementation. Children who received less than 34.25 kcal/day in supplement had more LEH than those who received more supplement. No differences in ossification status were found between supplementation groups. These data suggest that enamel formation may be more sensitive to changes in nutritional status than is bone mineralization. Disruptions of bone and enamel formation were both associated with frequent illness. Children who were ill more than 3.6% of the time had more LEH and fewer ossified hand-wrist centers than children who were less frequently ill. Conclusions regarding relative environmental sensitivity must take into account the specific aspects of dental and skeletal development examined. © 1993 Wiley-Liss, Inc.     

Prevalence and age at development of enamel hypoplasias in Mexican children

Enamel hypoplasias, deficiencies in enamel thickness resulting from disturbances during the secretory phase of enamel development, are generally believed to result from nonspecific metabolic and nutritional disruptions. However, data are scare on the prevalence and chronological distributions. of hypoplasias in populations experiencing mild to moderate malnutrition. The purpose of this article is to present baseline data on the prevalences and chronological distributions of enamel hypoplasias, by sex and for all deciduous and permanent anterior teeth, in 300 5 to 15-year-old rural Mexican children. Identification of hypoplasias was aided by comparison to a published standard (Federation Dentaire Internationale: Int. Dent. J. 32(2):159-167, 1982). The location of defects, by transverse sixths of tooth crowns, was used to construct distributions of defects by age at development. One or more hypoplasias were detected in 46.7% (95% CI = 40.9-52.5%) of children. Among the unworn and completely erupted teeth, the highest prevalence of defects was found on the permanent maxillary central incisors (44.4% with one or more hypoplasias), followed by the permanent maxillary canine (28.0%) and the remaining permanent teeth (26.2 to 22.2%) Only 6.1% of the completely erupted and unworn deciduous teeth were hypoplastic. The prevalence of enamel defects on the permanent teeth was up to tenfold greater than that found in studies of less marginal populations that used the FDI method. The prevalence of defects in transverse zones suggests a peak frequency of hypoplasias during the second and third years for the permanent teeth, corresponding to the age at weaning in this group. In the deciduous teeth, a smaller peak occurs between 30 and 40 weeks post gestation. The frequency of defects after three years of age is slightly higher in females than males, suggesting a sex difference in access to critical resources.     

Genetic Continuity of Bronze Age Ancestry with Increased Steppe-Related Ancestry in Late Iron Age Uzbekistan

Although Uzbekistan and Central Asia are known for the well-studied Bronze Age civilization of the Bactria–Margiana Archaeological Complex (BMAC), the lesser-known Iron Age was also a dynamic period that resulted in increased interaction and admixture among different cultures from this region. To broaden our understanding of events that impacted the demography and population structure of this region, we generated 27 genome-wide single-nucleotide polymorphism capture data sets of Late Iron Age individuals around the Historical Kushan time period (∼2100–1500 BP) from three sites in South Uzbekistan. Overall, Bronze Age ancestry persists into the Iron Age in Uzbekistan, with no major replacements of populations with Steppe-related ancestry. However, these individuals suggest diverse ancestries related to Iranian farmers, Anatolian farmers, and Steppe herders, with a small amount of West European Hunter Gatherer, East Asian, and South Asian Hunter Gatherer ancestry as well. Genetic affinity toward the Late Bronze Age Steppe herders and a higher Steppe-related ancestry than that found in BMAC populations suggest an increased mobility and interaction of individuals from the Northern Steppe in a Southward direction. In addition, a decrease of Iranian and an increase of Anatolian farmer-like ancestry in Uzbekistan Iron Age individuals were observed compared with the BMAC populations from Uzbekistan. Thus, despite continuity from the Bronze Age, increased admixture played a major role in the shift from the Bronze to the Iron Age in southern Uzbekistan. This mixed ancestry is also observed in other parts of the Steppe and Central Asia, suggesting more widespread admixture among local populations.     

Paradox and promise: Research on the role of recent advances in paleodemography and paleoepidemiology to the study of “health” in Precolumbian societies

Bioarcheology has made tremendous strides since the subdiscipline's inception, subsequent syntheses, the standardization of data collection methods, and analytical advances ranging from molecular analyses through age-estimation and biodistance. Concurrently, health and the adaptive success of past populations have remained primary concerns. However, questions are routinely raised about lesions and whether or not changing frequencies are synonymous with increases or decreases in stress, morbidity, and overall health. These include how and why healed lesions can simultaneously represent stress and survival, demanding that researchers understand how population dynamics influence skeletal sample formation. In this study, methods to analyze age- and sex-specific mortality patterns prior to, and in conjunction with, the analysis of linear enamel hypoplasias are demonstrated. Paleodemographic and paleoepidemiological models are presented for late Pre-Columbian skeletal samples from the Eastern Woodlands. Results of hazard modeling demonstrate that elevated mortality rates were commonplace during the latter half of the Mississippian period (AD 1200–1450) with reproductive-age females experiencing high age-specific risk of death attributed to the development of fortified villages and novel environments for increased pathogen loads. Corollary results are presented for the age-specificity of linear enamel hypoplasias in the central Illinois River valley. The epidemiological models demonstrate that the relationship between adult mortality and early childhood stress varied through space, culture, and time. These findings highlight the need to effectively operationalize measurements related to health and stress in past populations and support the adoption of selective mortality and heterogeneity in frailty as key concepts in bioarcheological research. Am J Phys Anthropol 155:268–280, 2014. © 2014 Wiley Periodicals, Inc.     

Cultivation and processing of Linum usitatissimum and Camelina sativa in southern Scandinavia during the Roman Iron Age

Charred seed conglomerates of Linum usitatissimum (flax) and Camelina sativa (gold of pleasure) were found at Uppåkra 2:25, a Roman Iron Age site in Skåne, southern Sweden. The conglomerates showed no mixing with each other, as they were almost pure flax and gold of pleasure respectively. Together with other archaeobotanical data from the site, they provide new evidence on the use, processing and cultivation of these two plants in early Iron Age in Scandinavia. Metric analyses were applied to flax seeds from both conglomerates and other contexts at this site, and compared to seed assemblages from other Roman Iron Age sites in Europe. The comparison showed that the flax cultivation at Uppåkra 2:25 was intended for the production of oil-rich seeds. The contextual relationship indicates that both flax and gold of pleasure seeds were processed in a similar way and used for oil. Furthermore, the pure seed conglomerate of gold of pleasure suggests that this plant was not a weed, but rather an intentionally grown crop which was cultivated separately from flax.     

The Genetic Origin of Daunians and the Pan-Mediterranean Southern Italian Iron Age Context

The geographical location and shape of Apulia, a narrow land stretching out in the sea at the South of Italy, made this region a Mediterranean crossroads connecting Western Europe and the Balkans. Such movements culminated at the beginning of the Iron Age with the Iapygian civilization which consisted of three cultures: Peucetians, Messapians, and Daunians. Among them, the Daunians left a peculiar cultural heritage, with one-of-a-kind stelae and pottery, but, despite the extensive archaeological literature, their origin has been lost to time. In order to shed light on this and to provide a genetic picture of Iron Age Southern Italy, we collected and sequenced human remains from three archaeological sites geographically located in Northern Apulia (the area historically inhabited by Daunians) and radiocarbon dated between 1157 and 275 calBCE. We find that Iron Age Apulian samples are still distant from the genetic variability of modern-day Apulians, they show a degree of genetic heterogeneity comparable with the cosmopolitan Republican and Imperial Roman civilization, even though a few kilometers and centuries separate them, and they are well inserted into the Iron Age Pan-Mediterranean genetic landscape. Our study provides for the first time a window on the genetic make-up of pre-Roman Apulia, whose increasing connectivity within the Mediterranean landscape, would have contributed to laying the foundation for modern genetic variability. In this light, the genetic profile of Daunians may be compatible with an at least partial autochthonous origin, with plausible contributions from the Balkan peninsula.     

A new approach to the study of Romanization in Britain: a regional perspective of cultural change in late iron age and roman dorset using the siler and gompertz-makeham models of mortality

This is the first study of health in the Roman Empire to use the Siler and Gompertz-Makeham models of mortality to investigate the health consequences of the 43 AD conquest of Britain. The study examined late Iron Age and Romano-British populations (N = 518) from Dorset, England, which is the only region of Britain to display continuity in inhumation burial practice and cemetery use throughout the two periods. Skeletal evidence for frailty was assessed using cribra orbitalia, porotic hyperostosis, periosteal lesions, enamel hypoplasia, dental caries, tuberculosis, and rickets. These health variables were chosen for analysis because they are reliable indicators of general health for diachronic comparison (Steckel and Rose: The backbone of history: health and nutrition in the western hemisphere (2002)) and are associated with the introduction of urbanism in Britain during the Roman period (Redfern: J Rom Archaeol Supp Series 64 (2007) 171-194; Redfern: Britannia 39 (2008a) 161-191; Roberts and Cox: Health and disease in Britain: from prehistory to the present day (2003)). The results show that levels of frailty and mortality were lower in the late Iron Age period, and no sex differences in mortality was present. However, post-conquest, mortality risk increased for children and the elderly, and particularly for men. The latter finding challenges received wisdom concerning the benefits of incorporation into the Empire and the higher status of the male body in the Roman world. Therefore, we conclude that the consequences of urbanism, changes in diet, and increased population heterogeneity negatively impacted health, to the extent that the enhanced cultural buffering of men did not outweigh underlying sex differences in biology that advantage women.     

Plant Resources from the Bronze Age and the first Iron Age in the northwestern arc of the Mediterranean Basin

This paper updates the question of plant resources during the Bronze Age and First Iron Age in the northwestern Mediterranean Basin. Among the cereals, six-row hulled barley is dominant throughout the territory, whereas naked and hulled wheats take on greater or lesser roles from region to region. Millet cultivation developed during the Bronze Age and became widespread in the First Iron Age. Apart from cereals, pulses, oil species and fruit appear to be secondary. Results from the study of archaeobotanical remains on wetland sites, however, lead us to question this finding, as oil plants and fruits are much better represented in waterlogged conditions. The cultivation of vine began in the First Iron Age. In spite of a number of characteristics common to plants throughout the study area, regional differences, evident in the Bronze Age, seem to dissipate in the First Iron Age.     

Health of infants in an Imperial Roman skeletal sample: perspective from dental microstructure

This study examines general health in the first year of life of a population of 127 subadults from the Imperial Roman necropolis of Isola Sacra (2nd-3rd century ACE). Health status was determined by analyzing 274 deciduous teeth from these children for Wilson bands (also known as accentuated striae), microscopic defects caused by a disruption to normal enamel development arising from some generalized external stressor. While macroscopic enamel defects, or hypoplasias, have long been used as proxies of general population health, we believe that this is the first population-wide study of microscopic defects in deciduous teeth. We used microstructural markers of enamel to attach very precise chronologies to Wilson band formation that allowed us to calculate maximum prevalence (MAP) and smoothed maximum prevalence (SMAP) distributions to portray what we believe to be a realistic risk profile for a past population of children. There appear to be two periods of high prevalence, the first beginning around age 2 months and continuing through month 5, and the second higher period beginning around month 6 and continuing through month 9. These results are discussed in light of historical records of Roman childhood rearing practices.     

Factors affecting the distribution of enamel hypoplasias within the human permanent dentition

Frequencies and morphological and chronological distributions of enamel hypoplasias are presented by tooth type (permanent I1 to M2s), based on a sample of 30 prehistoric Amerindians with complete and unworn dentitions. There is nearly a tenfold variation in frequency of defects by tooth, ranging from 0.13 per mandibular second molar to 1.27 per maxillary central incisor. The six anterior teeth average between 0.70 and 1.27 defects/tooth, whereas the eight posterior teeth average between 0.43 and 0.13 defects/tooth. Earlier developing teeth, such as incisors, have earlier peak frequencies of defects (2.0-2.5 years), while later developing teeth, such as second molars, have subsequent peak frequencies (5.0-6.0 years). These variations are relevant when comparing hypoplasia data based on different teeth. Differences in hypoplasia frequencies among teeth are not solely due to variation in time of crown development, as is usually reported. Rather, there is evidence for biological gradients in susceptibility to ameloblastic disruption. Anterior teeth are more hypoplastic than posterior teeth. More developmentally stable "polar" teeth are more hypoplastic than surrounding teeth. Polar teeth may be more susceptible to hypoplasias because their developmental timing is less easily disrupted. In all teeth, hypoplasias are most common in the middle and cervical thirds. Crown development and morphological factors, such as enamel prism length and direction, may influence the development and expression of enamel surface defects.     

Accessing Developmental Information of Fossil Hominin Teeth Using New Synchrotron Microtomography-Based Visualization Techniques of Dental Surfaces and Interfaces

Quantification of dental long-period growth lines (Retzius lines in enamel and Andresen lines in dentine) and matching of stress patterns (internal accentuated lines and hypoplasias) are used in determining crown formation time and age at death in juvenile fossil hominins. They yield the chronology employed for inferences of life history. Synchrotron virtual histology has been demonstrated as a non-destructive alternative to conventional invasive approaches. Nevertheless, fossil teeth are sometimes poorly preserved or physically inaccessible, preventing observation of the external expression of incremental lines (perikymata and periradicular bands). Here we present a new approach combining synchrotron virtual histology and high quality three-dimensional rendering of dental surfaces and internal interfaces. We illustrate this approach with seventeen permanent fossil hominin teeth. The outer enamel surface and enamel-dentine junction (EDJ) were segmented by capturing the phase contrast fringes at the structural interfaces. Three-dimensional models were rendered with Phong’s algorithm, and a combination of directional colored lights to enhance surface topography and the pattern of subtle variations in tissue density. The process reveals perikymata and linear enamel hypoplasias on the entire crown surface, including unerupted teeth. Using this method, highly detailed stress patterns at the EDJ allow precise matching of teeth within an individual’s dentition when virtual histology is not sufficient. We highlight that taphonomical altered enamel can in particular cases yield artificial subdivisions of perikymata when imaged using X-ray microtomography with insufficient resolution. This may complicate assessments of developmental time, although this can be circumvented by a careful analysis of external and internal structures in parallel. We further present new crown formation times for two unerupted canines from South African Australopiths, which were found to form over a rather surprisingly long time (> 4.5 years). This approach provides tools for maximizing the recovery of developmental information in teeth, especially in the most difficult cases.     

Congenital syphilis in the past: slaves at Newton Plantation, Barbados, West Indies.

Hutchinson's incisors and Moon's molars are specific lesions of congenital syphilis. The extensive but fragmentary clinical literature on these conditions describes reduced dimensions and thin enamel in the permanent incisors and first molars, crowding and infolding of the first molar cusps, notching of the upper incisors, and apical hypoplasias of the permanent canines. A Barbados slave cemetery (ca. 1660-1820 AD) includes three individuals with these features, suggesting a frequency at birth of congenital syphilis in the population approaching 10%. These three cases show triple the frequency of all hypoplasias and more than seven times the frequency of pitting hypoplasia present in the remainder of the series. The recognizable congenital syphilis cases account for much of the remarkably high frequency of hypoplasias in the series as a whole. We infer that syphilis contributed substantially to morbidity, infant mortality, and infertility in this population. Presence or absence of congenital syphilis may account for much of the variability in health and mortality seen among nineteenth century African-American populations.     

Madonna del Piano (Sesto Fiorentino, Florence, central Italy) ox and dog: a case of intentional Iron Age inhumation

Two almost complete and articulated skeletons of a small-sized 15-year-old shorthorn ox and of a 3-4-year-old dog were found associated to Iron Age human burials at Madonna del Piano, in Sesto Fiorentino, near Florence. The two skeletons were ritually buried. The find adds to another case of cattle burial also found in the area, and therefore attests to a penetration and persistence of late Neolithic and Bronze Age northern and eastern European practices in Italy. The specimens provide important evidence on the habits and believes of Iron Age circum-Mediterranean human populations. The ox reveals that castration was accomplished late in the animal’s growth, but also that cattle were used for heavy work, though being worshiped animals.     

Carbonized plant remains from a pre-Roman Iron Age house site at Opperdoes,West Friesland,The Netherlands

The eastern part of the region of West Friesland (The Netherlands) was densely inhabited in the Middle and Late Bronze Age (Hoogkarspel culture). In the whole of this area, Iron Age settlement has only been found around Opperdoes. Carbonized plant remains from features associated with a pre-Roman Iron Age house near Opperdoes are discussed and compared with Bronze Age data from the region. The evidence suggests that the Iron Age food economy was different from that in the Bronze Age. Barley and linseed were possibly imported, while gold-of-pleasure was cultivated at the site.     

The chronological distribution of enamel hypoplasias from prehistoric Dickson Mounds populations

The chronological distributions of enamel hypoplasias (indicators of nonspecific stress) are assessed for 111 individuals from two prehistoric populations from Dickson Mounds, Lewiston, Illinois. The earlier population (circa A.D. 950-1150) involves a transition from an indigenous gathering-hunting tradition to increasing adoption of Mississippian lifeways. The later population (circa A.D. 1150-1300) is fully Mississippian (MM). Based on the occurrence of hypoplasias on all permanent teeth except third molars, 14 half-year periods from birth to 7.0 years are graded for evidence of hypoplasia-stress. Both populations have a low frequency of hypoplasia which occur before 2 years of age and after 4 years of age. A common peak frequency of hypoplasias between 2.0 and 4.0 years is suggestive of an elevated degree of stress at weaning. The peak frequency of hypoplasias is earlier in the MM (2.5-3.0 years versus 3.0-3.5 years in the pre-Mississippian population). In addition, the rise to and decline from peak frequency occurs approximately 0.5 years earlier in the MM. The earlier and sharper rise to peak frequency suggests earlier and more severe weanling-related stress. Hypoplasias chronologies are undoubtedly influenced by age-related host resistance factors (Sarnat and Schour, 1941). Nevertheless, these data demonstrate that populations may vary in their chronological distribution of hypoplasias and that these variations may provide useful information on age-related patterns of exposure to environmental stressors.