Quantitative genetics of skeletal nonmetric traits in the rhesus macaques on Cayo Santiago. I. Single trait heritabilities

Exploring Kinship Within a Late Meroitic to Medieval Cemetery in Sudan Using k-Modes Clustering

OBJECTIVES

Intracemetery patterns at the Qinifab School site, a late Meroitic to Christian period cemetery (c. 250-1400 CE) between the fourth and fifth cataracts of the Nile River in Sudan, are modeled to explore the role of kinship in cemetery organization during significant sociopolitical and religious shifts.

MATERIALS AND METHODS

Sixty-eight cranial and 36 dental nonmetric traits were examined among 67 adults. A machine-learning clustering method (k-modes clustering algorithm), new to biological anthropology, was used to detect patterning among biological, demographic, and temporal data and validated with inter-individual Mahalanobis distances and mixed data principal components analysis using only biological data.

RESULTS

When three validated clusters were examined, a pattern emerged that aligned with the archaeological context of the cemetery when time period is considered. One cluster concentrated at the oldest end of the site appeared to be a founding group, with the other two groups equally comprising later periods. Some mortuary patterning by sex was visually identified; a few late to Post-Meroitic males grouped together in one cluster.

DISCUSSION

Individuals from Clusters 1 and 3 were buried near each other infrequently, which suggests two different kin groups may have intermarried with the third, or one group held a status that allowed identification with the other clusters. Kinship was not a determinant for males with archery items or individuals with incisor avulsion, as they were found in all three clusters. The Qinifab School cemetery reflects temporal organization, a multilocal residence pattern, and a lack of sex stratification for the medieval period.

Coming to the Caribbean: Eighty-five years of rhesus macaques (Macaca mulatta) at Cayo Santiago-A rare nonhuman primate model for the studies of adaptation, diseases, genetics, natural disasters, and resilience

The Cayo Santiago rhesus macaque colony represents one of the most important nonhuman primate resources since their introduction to the Caribbean area in 1938. The 85 years of continuing existence along with the comprehensive database of the rhesus colony and the derived skeletal collections have provided and will continue to provide a powerful tool to test hypotheses about adaptive and evolutionary mechanisms in both biology and medicine.

History of Health at Cayo Santiago-An Investigation of Environmental and Genetic Influences on the Skeletal Remains of the Introduced Rhesus Macaque (Macaca mulatta) Colony

The Cayo Santiago rhesus macaque colony is a renowned primate population that has experienced significant natural and anthropogenic ecological variation in their 85-year history. Demographic and familial information is also tracked and collated for the majority of monkeys. Thus, the health history of rhesus macaques at Cayo Santiago should reflect the impacts of both environmental and genetic factors. In this study, we utilized a sample of skeletal remains comprised of 2787 individuals (1571 females, 1091 males), born between 1938 and 2017 from the derived skeletal collection of the primate colony to assess variation in survivorship, pathology, bone mineral density (BMD), and dental eruption status, in the context of hurricane impacts, nutritional fluctuations, and matriline genealogy. Results demonstrated that rhesus macaques at Cayo Santiago exhibit a range of skeletal pathologies that encompass biomedical and archaeological significance, multiple etiologies, severities, locations, and types, in addition to a secular trend of declining BMD that is hypothesized to reflect decreasing physical activity levels under increasing population densities. Specifically, hurricane impacts were found to increase the rate of systemic disease, decrease BMD in young adults, and delay eruption of the primary dentition. Certain matrilines exhibited heightened levels of systemic disease at early ages while others exhibited greater rates of congenital disease. Early-life adversity, through the experience of major hurricanes, may enhance inflammatory pathways, heightening the risk of disease and accelerating the aging process leading to reduced BMD. Such impacts may underly greater levels of observed infection post-hurricane through intensification of pathogen transmission and disease rates brought on by hurricane-adaptive social strategies that favor closer proximity. Familial susceptibility to disease indicates heritable host genetic factors are likely influencing disease patterning in the population. A cluster of congenital diseases may most convincingly illustrate this, or alternatively reflects low levels of genetic diversity in the population.

Biological distances between Late Holocene hunter‐gatherers from the lower Paraná wetland (Argentina)

INTRODUCTION

This study assesses the biological affinity between Late Holocene hunter-gatherers that inhabited the region of the lower Paraná wetland (Argentina) at the end of the Late Holocene (1800-700 years BP).

METHODS

Cranial nonmetric traits were registered in 159 adult individuals of both sexes. Biodistances were estimated between environmental and archaeological units through Smith's Mean Measure of Divergence, Mahalanobis distance, multidimensional scaling, F_st index, and R-matrix. Biological distances concerning temporal and geographic distances between the archaeological sites were also evaluated through Mantel and partial Mantel tests.

RESULTS

The environmental units showed statistically significant biodistances according to a distance spatial pattern but low genetic differentiation between groups. Additionally, some archaeological sites with median radiocarbon dates around 700 years BP also presented statistically significant biodistances.

CONCLUSIONS

Gene flow and genetic drift could be responsible for the observed biodistance results. These processes gave rise to different subpopulations of hunter-gatherers with a shared material culture, whose territorial limits could have been reinforced around 700 years BP or earlier.

Genetic influences on dentognathic morphology in the Jirel population of Nepal

Patterns of genetic variation and covariation impact the evolution of the craniofacial complex and contribute to clinically significant malocclusions in modern human populations. Previous quantitative genetic studies have estimated the heritabilities and genetic correlations of skeletal and dental traits in humans and nonhuman primates, but none have estimated these quantitative genetic parameters across the dentognathic complex. A large and powerful pedigree from the Jirel population of Nepal was leveraged to estimate heritabilities and genetic correlations in 62 maxillary and mandibular arch dimensions, incisor and canine lengths, and post-canine tooth crown areas (N ≥ 739). Quantitative genetic parameter estimation was performed using maximum likelihood-based variance decomposition. Residual heritability estimates were significant for all traits, ranging from 0.269 to 0.898. Genetic correlations were positive for all trait pairs. Principal components analyses of the phenotypic and genetic correlation matrices indicate an overall size effect across all measurements on the first principal component. Additional principal components demonstrate positive relationships between post-canine tooth crown areas and arch lengths and negative relationships between post-canine tooth crown areas and arch widths, and between arch lengths and arch widths. Based on these findings, morphological variation in the human dentognathic complex may be constrained by genetic relationships between dental dimensions and arch lengths, with weaker genetic correlations between these traits and arch widths allowing for variation in arch shape. The patterns identified are expected to have impacted the evolution of the dentognathic complex and its genetic architecture as well as the prevalence of dental crowding in modern human populations.

Genetic variance in fitness indicates rapid contemporary adaptive evolution in wild animals

The rate of adaptive evolution, the contribution of selection to genetic changes that increase mean fitness, is determined by the additive genetic variance in individual relative fitness. To date, there are few robust estimates of this parameter for natural populations, and it is therefore unclear whether adaptive evolution can play a meaningful role in short-term population dynamics. We developed and applied quantitative genetic methods to long-term datasets from 19 wild bird and mammal populations and found that, while estimates vary between populations, additive genetic variance in relative fitness is often substantial and, on average, twice that of previous estimates. We show that these rates of contemporary adaptive evolution can affect population dynamics and hence that natural selection has the potential to partly mitigate effects of current environmental change.

The prevalence of under-nutrition among the tribal children in India: a systematic review

Tribal population of India constitutes 8.6% of the total population. They are more susceptible to undernutrition which is recognized as a prevalent health problem mainly because of their uncertainty of food supply, which has serious long term consequences for the child and adversely influences the development of the nation. The assessment of nutritional status is paramount importance because it impels to identify malnutrition which is an aggravation of morbidity and mortality. This review was aimed to find out the overall nutritional status of tribal preschool children. It also seek the major socio-cultural causes which influence the nutritional status from bio-cultural perspectives among the tribal children in India in order to make foundation of new research. In the present review, 41 papers on nutritional status of tribal preschool children published from January 1st 2000 till date, have been identified and included for analysis. To analyze the data, meta-analysis was done using MedCalc software.

The meta-analysis revealed the average rate of prevalence of underweight, stunting and wasting among the preschool tribal children of India was 42.96%; 44.82% and 23.69%. Among the 41 different studies these rates vary among the different tribal groups of different states associated with their socio-economic status (10%), their cultures of food consumption (10%), maternal education (15%), child feeding practices (20%), dietary deficit during pregnancy (25%) and poor nutrition of the child (52%).

Prevalence rate of under-nutrition and stunting is relatively high in comparison to WHO in India whereas, rate of wasting was lower in comparison to national level which reflect that immediate nutritional status was poor but chronic deficiency of nutrition was less. Nutritional education and short term appropriately planned nutritional intervention programs may also be useful for enhancing their nutritional status.

Non-metric traits, physiological stress indicators and paleopathological lesion on human skeletal remains from an early modern cemetery in Wyszyński Street, Wrocław, Poland (15th–18th centuries AD)

The anthropological analysis and assessment of the living conditions of historical populations should be comprehensive. Due to the scarcity of the well-preserved skeletal remains of a population buried at the cemetery in Wyszyński Street, Wrocław, each piece of information is particularly important in providing the complementary information about living and health conditions of late medieval and early modern inhabitants of Wrocław. This study aims to assess the living conditions of the late medieval and early modern Wrocław inhabitants. This aim was reached by analyzing the frequency of non-metrical cranial and postcranial traits, physiological stress indicators, and pathological lesions. The importance of these traits for population studies is also discussed. For 98 skeletons (22.4% male and 37.8% female) from a cemetery located in Wyszyński Street, (15th –18th centuries AD), the frequencies (p) of the following traits were analyzed: 38 non-metric cranial and 9 post-cranial traits, the morphological indicators of physiological stress (i.e. cribra orbitalia and enamel hypoplasia), caries and pathological lesions on bones. Among the non-metric cranial traits, only nine (23.7%) were not observed. The most frequent (from p= 0.30 to p=0.65) were foramen parietale, incisura frontalis accesoria seu foramen frontale accesorius, foramen supraorbitale, M3 mandibulare, ossicula suturae lambdoideae, and foramen mastoideum extrasuturale. Only three non-metric post-cranial traits were observed, but with low frequency (p=0.01 and 0.02). Cribra orbitalia was present in 37.0% of the skeletons while enamel hypoplasia was present in only 2.6%. Susceptibility to caries occurred in 68% of the cases while carries lesions occurred in 31.2%. Among pathological changes, the most frequent were degenerative changes (21.6%) and injuries (19.6%). Owing to the poorly preserved remains, the complete assessment of the living conditions of the population was difficult. The number of the observed traits would have probably increased, had the number of complete and well-preserved skeletons been higher. The results of the study suggest that the living conditions of the studied population were poor. It is hypothesized that the cemetery was a burial place for prisoners and victims of various epidemics that affected the city. But since the historical sources of this cemetery are scarce, it is hard to unequivocally state its purpose with certainty.

Non-metric traits and anatomical variants that can mimic trauma in the human skeleton

This paper presents some of the more commonly encountered non-metric traits and minor anatomical variants in the adult human skeleton that can mimic or be mistaken for trauma. Distinguishing non-metric traits is contingent upon both a knowledge of potential non-metric traits as well as the normal developmental timing, location, and anatomy of maturational markers in the human skeleton. Distinguishing non-metric traits from trauma in dry bone is an essential component in establishing an accurate and thorough forensic analysis of human remains, especially as it deals with antemortem and perimortem trauma, and postmortem damage.

Genetic contributions to dental dimensions in brown-mantled tamarins (Saguinus fuscicollis) and rhesus macaques (Macaca mulatta)

OBJECTIVES

The use of dental metrics in phylogenetic reconstructions of fossil primates assumes variation in tooth size is highly heritable. Quantitative genetic studies in humans and baboons have estimated high heritabilities for dental traits, providing a preliminary view of the variability of dental trait heritability in nonhuman primate species. To expand upon this view, the heritabilities and evolvabilities of linear dental dimensions are estimated in brown-mantled tamarins (Saguinus fuscicollis) and rhesus macaques (Macaca mulatta).

MATERIALS AND METHODS

Quantitative genetic analyses were performed on linear dental dimensions collected from 302 brown-mantled tamarins and 364 rhesus macaques. Heritabilities were estimated in SOLAR using pedigrees from each population, and evolvabilities were calculated manually.

RESULTS

Tamarin heritability estimates range from 0.19 to 0.99, and 25 of 26 tamarin estimates are significantly different from zero. Macaque heritability estimates range from 0.08 to 1.00, and 25 out of 28 estimates are significantly different from zero.

DISCUSSION

Dental dimensions are highly heritable in captive brown-mantled tamarins and free-ranging rhesus macaques. The range of heritability estimates in these populations is broadly similar to those of baboons and humans. Evolvability tends to increase with heritability, although evolvability is high relative to heritability in some dimensions. Estimating evolvability helps to contextualize differences in heritability, and the observed relationship between evolvability and heritability in dental dimensions requires further investigation.

Additive genetic variation in the craniofacial skeleton of baboons (genus Papio) and its relationship to body and cranial size

OBJECTIVES

Determining the genetic architecture of quantitative traits and genetic correlations among them is important for understanding morphological evolution patterns. We address two questions regarding papionin evolution: (1) what effect do body and cranial size, age, and sex have on phenotypic (V_P ) and additive genetic (V_A ) variation in baboon crania, and (2) how might additive genetic correlations between craniofacial traits and body mass affect morphological evolution?

MATERIALS AND METHODS

We use a large captive pedigreed baboon sample to estimate quantitative genetic parameters for craniofacial dimensions (EIDs). Our models include nested combinations of the covariates listed above. We also simulate the correlated response of a given EID due to selection on body mass alone.

RESULTS

Covariates account for 1.2-91% of craniofacial V_P . EID V_A decreases across models as more covariates are included. The median genetic correlation estimate between each EID and body mass is 0.33. Analysis of the multivariate response to selection reveals that observed patterns of craniofacial variation in extant baboons cannot be attributed solely to correlated response to selection on body mass, particularly in males.

DISCUSSION

Because a relatively large proportion of EID V_A is shared with body mass variation, different methods of correcting for allometry by statistically controlling for size can alter residual V_P patterns. This may conflate direct selection effects on craniofacial variation with those resulting from a correlated response to body mass selection. This shared genetic variation may partially explain how selection for increased body mass in two different papionin lineages produced remarkably similar craniofacial phenotypes.

Heritability of the Human Craniofacial Complex

Quantifying normal variation and the genetic underpinnings of anatomical structures is one of the main goals of modern morphological studies. However, the extent of genetic contributions to normal variation in craniofacial morphology in humans is still unclear. The current study addresses this gap by investigating the genetic underpinnings of normal craniofacial morphology. The sample under investigation consists of 75 linear and angular measurements spanning the entire craniofacial complex, recorded from lateral cephalographs of 1,379 participants in the Fels Longitudinal Study. Heritabilities for each trait were estimated using SOLAR, a maximum-likelihood variance components approach utilizing all pedigree information for parameter estimation. Trait means and mean effects of the covariates age, sex, age(2) , sex × age, and sex × age(2) were simultaneously estimated in the analytic models. All traits of the craniofacial complex were significantly heritable. Heritability estimates ranged from 0.10 to 0.60, with the majority being moderate. It is important to note that we found similar ranges of heritability occurring across the different functional/developmental components of the craniofacial complex, the splanchnocranium, the basicranium, and the neurocranium. This suggests that traits from different regions of the craniofacial complex are of comparable utility for the purposes of population history and phylogeny reconstruction. At the same time, this genetic influence on craniofacial morphology signals a caution to researchers of nongenetic studies to consider the implications of this finding when selecting samples for study given their project design and goals.

Free-ranging Cayo Santiago rhesus monkeys (Macaca mulatta): III. Dental eruption patterns and dental pathology

This article describes the dental eruption patterns, dentition, and dental wear, including tooth loss and breakage, of the free-ranging population of rhesus monkeys (Macaca mulatta) on Cayo Santiago (CS), Puerto Rico, ranging from 24 hr to 25 years old. Of the 694 monkeys on the island in the year 1985, 688 (99.1%; 366 males, 322 females) were captured and the dentition of 685 subjects (98.7% of the total population; 366 males, 319 females) was examined. Animals ranged in age from less than 24 hr to 331 months (27.58 years), encompassing the entire life span of the CS macaques. Results demonstrated that the first deciduous teeth appeared as early as the third day of life and that the sequence of dental eruption was comparable to the pattern observed in laboratory rhesus. However, there were slight differences in the age of eruption of individual teeth. For example, the canines and third molars erupted about a year later in the CS macaques compared to some laboratory rhesus. Overall, CS rhesus had good oral health and dental condition although tooth wear, loss, and breakage were common in aged animals, especially in males. This report, combined with earlier studies on morphological characteristics and skeletal remains of the CS macaques, provides the basis for further studies on the biology, genetics, life history, and effects of the environment on rhesus monkeys.

Occurrence of the Uto-Aztecan premolar trait in a contemporary Colombian Amerindian population

In 2009, in the Indian Kamëntša community in southern Colombia an oral inspection was conducted on 61 young people. Using the methods of Arizona State University's Dental Anthropology System (ASUDAS) the presence of unilateral Uto-Aztecan premolar (UAP) is reported here.

Relationship of cranial robusticity to cranial form, geography and climate in Homo sapiens

Variation in cranial robusticity among modern human populations is widely acknowledged but not well-understood. While the use of "robust" cranial traits in hominin systematics and phylogeny suggests that these characters are strongly heritable, this hypothesis has not been tested. Alternatively, cranial robusticity may be a response to differences in diet/mastication or it may be an adaptation to cold, harsh environments. This study quantifies the distribution of cranial robusticity in 14 geographically widespread human populations, and correlates this variation with climatic variables, neutral genetic distances, cranial size, and cranial shape. With the exception of the occipital torus region, all traits were positively correlated with each other, suggesting that they should not be treated as individual characters. While males are more robust than females within each of the populations, among the independent variables (cranial shape, size, climate, and neutral genetic distances), only shape is significantly correlated with inter-population differences in robusticity. Two-block partial least-squares analysis was used to explore the relationship between cranial shape (captured by three-dimensional landmark data) and robusticity across individuals. Weak support was found for the hypothesis that robusticity was related to mastication as the shape associated with greater robusticity was similar to that described for groups that ate harder-to-process diets. Specifically, crania with more prognathic faces, expanded glabellar and occipital regions, and (slightly) longer skulls were more robust than those with rounder vaults and more orthognathic faces. However, groups with more mechanically demanding diets (hunter-gatherers) were not always more robust than groups practicing some form of agriculture.

An examination of Nubian and Egyptian biological distances: support for biological diffusion or in situ development?

Many authors have speculated on Nubian biological evolution. Because of the contact Nubians had with other peoples, migration and/or invasion (biological diffusion) were originally thought to be the biological mechanism for skeletal changes in Nubians. Later, a new hypothesis was put forth, the in situ hypothesis. The new hypothesis postulated that Nubians evolved in situ, without much genetic influence from foreign populations. This study examined 12 Egyptian and Nubian groups in an effort to explore the relationship between the two populations and to test the in situ hypothesis. Data from nine cranial nonmetric traits were assessed for an estimate of biological distance, using Mahalanobis D(2) with a tetrachoric matrix. The distance scores were then input into principal coordinates analysis (PCO) to depict the relationships between the two populations. PCO detected 60% of the variation in the first two principal coordinates. A plot of the distance scores revealed only one cluster; the Nubian and Egyptian groups clustered together. The grouping of the Nubians and Egyptians indicates there may have been some sort of gene flow between these groups of Nubians and Egyptians. However, common adaptation to similar environments may also be responsible for this pattern. Although the predominant results in this study appear to support the biological diffusion hypothesis, the in situ hypothesis was not completely negated.

The frequency of metopism in Anatolian populations dated from the Neolithic to the first quarter of the 20th century

Metopism, which is defined as a condition in which the two pieces of the frontal bone fail to merge in early childhood, displays varying degrees of incidence. In this study, the variation of the frequency of metopism across historical periods is investigated on the skulls of 487 adults from 12 different Ancient Anatolian populations dated to various periods of history ranging from the Neolithic to the first quarter of the 20th century. In addition, the study also examines the relationship of metopism to sex and cranial form. It is revealed that the frequency of metopism showed a relative increase across time periods in Anatolia after the Neolithic Period, with the exception of the Cevizcioğlu Ciftliği population. However, no significant relationship was found between metopism and cranial form or sex. It is found that the frequency of metopism in Ancient Anatolia had a distribution range of 3.3-14.9%. This distribution shows that the inhabitants of Anatolia have a heterogeneous genetic make-up due to the geographical situation of Anatolia, which has been open to gene flow both in the past and at present.

A genomewide linkage scan for quantitative trait loci influencing the craniofacial complex in baboons (Papio hamadryas spp.)

Numerous studies have detected significant contributions of genes to variation in development, size, and shape of craniofacial traits in a number of vertebrate taxa. This study examines 43 quantitative traits derived from lateral cephalographs of 830 baboons (Papio hamadryas) from the pedigreed population housed at the Southwest National Primate Research Center. Quantitative genetic analyses were conducted using the SOLAR analytic platform, a maximum-likelihood variance components method that incorporates all familial information for parameter estimation. Heritability estimates were significant and of moderate to high magnitude for all craniofacial traits. Additionally, 14 significant quantitative trait loci (QTL) were identified for 12 traits from the three developmental components (basicranium, splanchnocranium, and neurocranium) of the craniofacial complex. These QTL were found on baboon chromosomes (and human orthologs) PHA1 (HSA1), PHA 2 (HSA3), PHA4 (HSA6), PHA11 (HSA12), PHA13 (HSA2), PHA16 (HSA17), and PHA17 (HSA13) (PHA, P. hamadryas; HSA, Homo sapiens). This study of the genetic architecture of the craniofacial complex in baboons provides the groundwork needed to establish the baboon as an animal model for the study of genetic and nongenetic influences on craniofacial variation.

The influence of artificial cranial vault deformation on the expression of cranial nonmetric traits: its importance in the study of evolutionary relationships

Nonmetric cranial traits have been commonly used in evolutionary relationship studies. They develop during the growth and development of an individual, and for this reason its expression presents different sources of genetic and nongenetic variation. However, the use of these features in evolutionary relationship studies carries the implicit assumption that much of the nonmetric trait variation is essentially genetic. Among the nonheritable factors, cranial vault deformation has been the most studied in human populations. Because of the widespread distribution and elevated rate of artificial cranial vault deformation found in America, and the importance of nonmetric traits in evolutionary relationship studies in this area, the objectives of this paper are as follows: (a) to study the influence of artificial cranial vault deformation on the presence of nonmetric traits within samples of human craniofacial remains; and (b) to establish artificial cranial vault deformation influence on evolutionary relationships between local populations on a regional scale. Our results indicate that artificial cranial vault deformations alter the variation and covariation of metric and nonmetric traits in some samples. Wormian bones, placed in cranial vault sutures, are the most influenced by this factor. However, our results suggest that when all nonmetric traits were used the artificial cranial vault deformation did not influence the basic pattern of variation among samples. The exclusion or inclusion of wormians bones in evolutionary relationships analysis did not modify the results, but using only wormians bones lead to inconsistent results indicating that these traits have little value on these kind of studies.

Biological divergence and equality during the first millennium BC in human populations of central Italy

The frequencies of nine discrete cranial traits are contrasted among 10 skeletal series of central Italy to assess the patterning of biological affinity or divergence. In this study various statistical applications were used: Mean Measure of Divergence (MMD), which was elaborated using the WPGMA cluster analysis, neighbor-joining method and principal coordinate analysis. The results show two main groups divided by the Apennines, which probably were a geographic barrier to biological exchange during the Italian Iron Age. This fact induced endogamous phenomena in the populations on the two sides of Italy (Adriatic and Tyrrenian) and probably increased the familial segregation of traits. The group on the western side has a further division between samples of the central coast and those of the southern coast. The latter samples seem to be more closely connected to Sardinian peoples, and this indicates gene flow and cultural contacts, which were not hindered by the sea. This segregation appears to have receded by Roman times.

Why are rare traits unilaterally expressed?: Trait frequency and unilateral expression for cranial nonmetric traits in humans

Based on an analysis of nonmetric trait databases from several large skeletal series in Northern Europe and South America, representing 27 bilateral traits, we report a predictable relationship between the frequency of nonmetric traits and the probability that they are expressed bilaterally. In a wider sampling of traits and populations, this study thus confirms the findings of an earlier study by Ossenberg ([1981] Am. J. Phys. Anthropol. 54:471-479), which reported the same relationship for two mandibular traits. This trend was previously explained by extending the multifactorial threshold model for discontinuous traits to incorporate either separate thresholds for unilateral or bilateral expression, or by a fuzzy threshold in which the probability of bilateral expression increases away from the median threshold value. We show that the trend is produced under the standard multifactorial threshold model for discontinuous traits simply if the within-individual or developmental instability variance remains relatively constant across the range of liability. Under this assumption, the number of individuals in which one side but not the other is pushed over the threshold for trait formation will be a larger proportion of the number of individuals expressing the trait when the trait frequency is low. As trait frequency increases, the significance of within-individual variance as a determinant of trait formation decreases relative to the genetic and among-individual environmental variance. These results have implications for interpreting nonmetric trait data as well as for understanding the prevalence of unilateral vs. bilateral expression of a wide variety of discontinuous traits, including dysmorphologies in humans.

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.

Nonmetric cranial trait variation and prehistoric biocultural change in the Azapa Valley, Chile

Historically, interpretations of both biological and cultural change within the prehistoric Azapa Valley, northern Chile, have cited large-scale population movements, with replacement from complex societies located in the adjacent highlands to the east. Biological estimates of this change have traditionally relied upon biodistance estimates, using craniofacial measures of both deformed and nondeformed skulls. In order to evaluate whether large-scale prehistoric migrations occurred in the Azapa Valley, we examine biodistance results from nonmetric cranial traits for eight mortuary samples that represent all time periods of prehistoric occupation of the valley. None of the mean measures of divergences (MMD) among mortuary samples examined by this study were significant. These results suggest biological continuity in the Azapa Valley during 5,000 years of prehistory, with nonsignificant gene flow during the late Middle Horizon (AD 750-1100) and Late Intermediate (AD 1100-1476) periods. Biodistance results also suggest endogamy within coastal and inland populations. The broader implications of these results are discussed.

Assessing non-metric skeleton characters as a morphological tool

The appearance of non-metric skeletal characters in vertebrates results mainly from basic genetic control, as proved and documented for house mice and humans. Although the heritability of non-metric traits, mainly the presence of foramina and similar structures for blood vessels and nerves or dental occlusal variants, have been evaluated as rather low, the simultaneous consideration of several traits allows estimation of epigenetic variation in time and space as a result of genetic relationship. Thus, the main use of non-metric characters has been aimed at assessing epigenetic variability and divergence among populations. Applications extend from the problem of genetic isolation of populations, the lack of reproductive contact, detection of genetic drift, systematic studies to clarify species taxonomy, to phylogenetic interpretation. Additionally, non-directional deviations from bilateral symmetry in non-metric characters, e.g. fluctuating asymmetry, could be caused by current environmental conditions in general. Fluctuating asymmetry is regarded as a measure of developmental instability to indicate the presence of genomic changes or the influence of contamination and/or habitat deterioration, and is also used as a further population parameter with integrated information. However, standpoints on the use of fluctuating asymmetry are quite inconsistent, fluctuating themselves between considering it a powerful biomonitoring tool to being merely a curious scientific toy.

The value of infracranial nonmetric variation in studies of modern Homo sapiens: an Australian focus

The value of quantitative infracranial nonmetric variation is examined in the study of population relationships by using samples from populations originating from five major geographic regions: Australia (two populations), Africa, East Asia, Europe, and Polynesia. According to the nonspecificity hypothesis, there are no distinct large classes of genes affecting one group of attributes exclusively; thus infracranial nonmetric traits should compare with other osteologic data sets in addressing questions of population relationships. By using the mean measure of divergence, infracranial nonmetric traits are shown to be useful in separating populations, particularly when using female and pooled-sex samples. The two Australian female samples (New South Wales coastal Australian and South Australian Aboriginals) are shown to be closer than any other two samples. The picture of intrapopulation and interpopulation variation in infracranial nonmetric traits is extended and clarified. Distance studies with infracranial nonmetric traits are possible but more illuminating if the sexes are first separated. Infracranial nonmetric variation does extend the knowledge of human population studies in yielding biologically meaningful results relating to development and ontogeny.

Sutural bone frequency in synostotic rabbit crania

This study tests the hypothesis that crania with synostosed sutures will have a significantly higher incidence of calvarial sutural bones than normal crania. Sutural bones were counted in seven calvarial sutures and compared among four groups of adult New Zealand white rabbit skulls: normal in-colony (NI) controls (N = 14), normal out-colony (NO) controls (N = 12), skulls with familial delayed onset (DO) coronal synostosis (N = 25), and skulls with experimentally immobilized coronal sutures (EI) (N = 20). Comparisons among groups were made with a Kruskal-Wallis one-way ANOVA and between groups with a Mann-Whitney U-test, using a Bonferroni correction for multiple comparisons. Significant differences (P < 0.05) were noted only in the coronal and sagittal sutures, with EI crania having the greatest number of coronal sutural bones; between group differences were undetectable for sagittal sutural bones. A post hoc two-sample binomial test for equal proportions showed that the distribution of coronal sutural bones among individuals across groups was even, while the distribution of sagittal sutural bones was significantly higher in EI crania. These results suggest that altered sutural forces of the calvaria contribute to an increased occurrence of sutural bones. However, the influence of inheritance on increased occurrence of sutural bones cannot be discounted, as reflected in the equivalent number of individuals across groups that possessed coronal sutural bones.

Concordance of cranial and dental morphological traits and evidence for endogamy in ancient Egypt

A biological affinities study based on frequencies of cranial nonmetric traits in skeletal samples from three cemeteries at predynastic Naqada, Egypt, confirms the results of a recent nonmetric dental morphological analysis. Both cranial and dental traits analyses indicate that the individuals buried in a cemetery characterized archaeologically as high status are significantly different from individuals buried in two other, apparently nonelite cemeteries and that the nonelite samples are not significantly different from each other. A comparison with neighbouring Nile Valley skeletal samples suggests that the high status cemetery represents an endogamous ruling or elite segment of the local population at Naqada, which is more closely related to populations in northern Nubia than to neighbouring populations in southern Egypt.

Cranial deformation and nonmetric trait variation

Cranial deformation is known to influence many traditional craniometric variables, but its effects on nonmetric trait variation are not well characterized. In this study, we examine the effects of three types of deformation (annular, lambdoid flattening, and fronto-occipital) on nonmetric traits, using a large sample of protohistoric and prehistoric crania. Our results indicate that a few traits are increased or decreased in relative frequency by particular types of deformation, but that these effects have little impact on the calculation of biological distances between groups.