Why Are Rare Traits Unilaterally Expressed?: Trait Frequency and Unilateral Expression for Cranial Non-Metric Traits in Humans. Benedikt Hallgrímsson, Barra Ó Donnabháin, Deborah E. Blom, Maria C. Lozada, and Katherine Willmore. American Journal of Physical Anthropology, 128(1): 14-25, 2005. (original) (raw)
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American Journal of Physical Anthropology, 2005
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
An examination of the meaning of cranial discrete traits for human skeletal biological studies
American Journal of Physical Anthropology, 1974
Discrete traits are of increasing interest in comparative skeletal biological research. Characteristics justifying their use have been investigated primarily in mice, however. Using 72 discrete variants, 321 human skulls from the Terry Collection of known race, sex and age have been studied. Significant sex and age differences were detected. Inter-trait correlation was found to be at a low but significant overall level. Multivariate comparison with conventional craniometric analysis was undertaken on subdivisions of the sample, and distances based on metric and nonmetric data were concordant. It is concluded, on the basis of these findings and the discontinuous variant frequency distributions, that discrete traits in isolation are not of paramount value to skeletal genetic studies, but may be vital in comparison and conjunction with other types of data in analyzing the population genetics of extinct groups.
Relationships between non-metric skeletal traits and cranial size and shape
American Journal of Physical Anthropology, 1979
A long-standing controversy exists about the comparative utility of metric and non-metric traits as biological indicators in population studies. We hypothesize that the underlying scale which determines the presence or absence of a cranial non-metric trait is an expression of general and/or local size variation in the cranium. Therefore metric and non-metric traits will share a common developmental determination. The hypothesis implies that the underlying scale of a non-metric trait will be correlated with measures of cranial size and shape. Forty-eight cranial metric and twenty-five cranial nonmetric traits were scored on the left side of adult male crania from four North American Indian populations. New threshold traits were generated for each non-metric trait by dichotomizing discriminant scores produced by discriminant function analysis. The discriminant analysis was performed using metric traits to discriminate between groups formed by non-metric trait presence or absence. Every non-metric trait tested was significantly correlated with its threshold trait in a t least one population. The correlations were of moderate to high levels depending on the trait and population sample studied. This implies that metric and non-metric traits share a moderate to high degree of developmental determination. The cause of these correlations may lie in the common effects that growth and development of the soft tissue and functional spaces of the cranium exert on both metric and non-metric traits. The relative worth of metric and non-metric skeletal variants in studies of biological relationship has been debated ever since Berry and Berry ('67) asserted the superiority of non-metric traits for population comparisons. Several workers (e.g., Rightmire, '72; Reichs, '72; Gaherty, '74; Corruccini, '74; Carpenter, '76; Ossenberg, '77) have attempted to settle this dispute by comparing biological distances derived from metric and non-metric traits with models based on cultural and/or geographic separation. The results of these studies are equivocal. Rightmire ('72) and Carpenter ('76) found metric distances provided the best fit to their cultural models, while Gaherty ('741, Reichs ('721, and Ossenberg ('77) found that non-metric distances fit
American journal of …, 2010
To date, differences in craniofacial robusticity among modern and fossil humans have been primarily addressed by analyzing adult individuals; thus, the developmental basis of such differentiation remains poorly understood. This article aims to analyze the ontogenetic development of craniofacial robusticity in human populations from South America. Geometric morphometric methods were used to describe cranial traits in lateral view by using landmarks and semilandmarks. We compare the patterns of variation among populations obtained with subadults and adults to determine whether population-specific differences are evident at early postnatal ontogeny, compare ontogenetic allometric trajectories to ascertain whether in Wiley InterScience (www.interscience.wiley.com).
Scoring of nonmetric cranial traits: a population study
Journal of Anatomy, 1999
The aims of the present study were : (1) to supply further knowledge about variations in nonmetric cranial traits in relation to sex, age and laterality and (2) to evaluate biological distance between samples from a recent population. The incidence of 18 nonmetric variants of the cranium were determined in 3 adult samples of 394 skulls of known sex from North Sardinia (Sassari, Alghero and Ozieri) ; for the Sassari sample (n l 200) age at death was also known. Some significant sex differences were observed. Age did not appear to influence the frequency of the discontinuous traits but did for legibility. Side differences may provide important information about environmental influences. The interpopulation analysis indicates a stronger relationship between samples that are geographically closer (Sassari and Alghero), in accordance with other studies, strengthening the hypothesis of the validity of the use of nonmetric traits in the study of the peopling of a territory.
Heritability of human cranial dimensions: comparing the evolvability of different cranial regions
2009
Abstract Quantitative craniometrical traits have been successfully incorporated into population genetic methods to provide insight into human population structure. However, little is known about the degree of genetic and non-genetic influences on the phenotypic expression of functionally based traits. Many studies have assessed the heritability of craniofacial traits, but complex patterns of correlation among traits have been disregarded. This is a pitfall as the human skull is strongly integrated.
Cranial deformation and nonmetric trait variation
American Journal of Physical Anthropology, 1993
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