John M. Lynch

Quantifying temporal bone morphology of great apes and humans: an approach using geometric morphometrics

The hominid temporal bone offers a complex array of morphology that is linked to several different functional systems. Its frequent preservation in the fossil record gives the temporal bone added significance in the study of human evolution, but its morphology has proven difficult to quantify. In this study we use techniques of 3D geometric morphometrics to quantify differences among humans and great apes and discuss the results in a phylogenetic context. Twenty‐three landmarks on the ectocranial surface of the temporal bone provide a high level of anatomical detail. Generalized Procrustes analysis (GPA) is used to register (adjust for position, orientation and scale) landmark data from 405 adults representing Homo, Pan, Gorilla and Pongo. Principal components analysis of residuals from the GPA shows that the major source of variation is between humans and apes. Human characteristics such as a coronally orientated petrous axis, a deep mandibular fossa, a projecting mastoid process, and reduced lateral extension of the tympanic element strongly impact the analysis. In phenetic cluster analyses, gorillas and orangutans group together with respect to chimpanzees, and all apes group together with respect to humans. Thus, the analysis contradicts depictions of African apes as a single morphotype. Gorillas and orangutans lack the extensive preglenoid surface of chimpanzees, and their mastoid processes are less medially inflected. These and other characters shared by gorillas and orangutans are probably primitive for the African hominid clade.

Geometric morphometrics in primatology : Craniofacial variation in Homo sapiens and Pan troglodytes

Traditionally, morphometric studies have relied on statistical analysis of distances, angles or ratios to investigate morphometric variation among taxa. Recently, geometric techniques have been developed for the direct analysis of landmark data. In this paper, we offer a summary (with examples) of three of these newer techniques, namely shape coordinate, thin-plate spline and relative warp analyses. Shape coordinate analysis detected significant craniofacial variation between 4 modern human populations, with African and Australian Aboriginal specimens being relatively prognathous compared with their Eurasian counterparts. In addition, the Australian specimens exhibited greater basicranial flexion than all other samples. The observed relationships between size and craniofacial shape were weak. The decomposition of shape variation into affine and non-affine components is illustrated via a thin-plate spline analysis of Homo and Pan cranial landmarks. We note differences between Homo and Pan in the degree of prognathism and basicranial flexion and the position and orientation of the foramen magnum. We compare these results with previous studies of these features in higher primates and discuss the utility of geometric morphometrics as a tool in primatology and physical anthropology. We conclude that many studies of morphological variation, both within and between taxa, would benefit from the graphical nature of these techniques.

Risk Factors Associated With Deformational Plagiocephaly

OBJECTIVE: This study was designed to statistically evaluate the independent and interacting effects of biological and environmental risk factors that influence lateralization of deformational plagiocephaly (DP) in an attempt to provide future guidance for clinical treatment. METHODS: A database of >20000 children treated for DP was examined by using 2- and 3-way factor analyses for categorical frequency data, representing the largest statistical analysis of DP to date. Data on parity, zygosity, intrauterine presentation, birth number and weight, sleep position, lateralization, and sex were collected from parents of children with DP who were treated at Cranial Technologies, Inc, from 1990 to 2007. RESULTS: As with most DP studies, male patients were significantly overrepresented. Nonetheless, after statistically accounting for sex in our analyses, DP is significantly correlated with primiparity, fewer vertex but more breech and transverse intrauterine presentations, twinning (specifically, dizygosity), and, finally, right-sided lateralization. Additional analyses revealed that several factors correlated with DP, such as intrauterine presentation, sleep position, and lateralization, are not easily explained by an underlying biological factor. Instead, sleep position was the single greatest predictor of lateralization. CONCLUSION: Although previous studies have argued for both environmental and underlying biological factors associated with DP, we found that lateralization in children with DP could be largely explained by environmental factors such as sleep position.

Use of Geometric Morphometrics to Differentiate Gila (Cyprinidae) within the Upper Colorado River Basin

Abstract Video images of 215 adult Gila robusta and 148 endangered Gila cypha were collected from May 1991–October 1992 at eight Colorado River basin localities (seven upper basins and one lower basin). The two species were sympatric at five of these locations; G. robusta was absent at one site, whereas G. cypha was missing at two others. Saggital views of each individual were videotaped and 25 morphological points (15 anatomical landmarks and 10 helping points) identified. Bookstein shape coordinates were calculated from Cartesian coordinates of these landmarks and points, whereas centroid size was used as a measure of body size. Shape differences were evaluated among populations of each species using MANOVA and canonical variates analysis. In G. cypha, variation encompassed three aspects: nuchal hump (most pronounced in Grand Canyon forms), relative head size (larger in Cataract Canyon forms), and caudal peduncle dimensions (shorter with a tapering depth in Cataract Canyon forms but longer and uniformly deeper in those from Desolation Canyon). Nuchal development in G. robusta is slight, hence only head and peduncle dimensions distinguished populations. Those individuals from Cataract Canyon had relatively shorter peduncles that (again) tapered in depth from anterior to posterior, whereas G. robusta from Desolation Canyon possessed peduncles that were much longer and of uniform depth. Specimens from Debeque and Rifle Canyons had proportionally smaller heads. Variation among all 13 populations (i.e., both species together) was evaluated using relative warp analysis, with G. cypha and G. robusta clearly separated at all sympatric locations except those from Desolation and Caratact Canyons. Here, body shapes of the two species converged. Overall, shape variation in both species is clinal. Although results from our geometric morphometric analysis were statistically similar to those based on distances derived from a truss analysis, the geometric approach visually demonstrated phenotypic differences among populations and species and this, in turn, has management implications.

Sexual Dimorphism in the Craniofacial Skeleton of Modern Humans

Sexual dimorphism is a major component of infraspecific variation in nonhuman primates. Among humans, differences in the pattern and degree of sexual dimorphism may provide a means for discriminating between populations. In this paper we explore the variance dimorphism, sex-specific size and shape differences, and between-population differences in patterns of sexual dimorphism in a sample of Romano—British (n = 47) and modern African (n = 53) crania. Shape coordinates, uniform components of variation and centroid size were derived for nine midsagittal landmarks obtained from lateral radiographs of the skull. No evidence was found for size-variance or shape-variance dimorphism in either population. Significant sexual size dimorphism was detected in the Romano—British sample alone. No significant sexual dimorphism in uniform components of variation was found in either sample. Multivariate analyses of variance for the effect of sex on shape coordinate pairs detected significant variation in the African sample, particularly in those landmarks that measure the amount of prognathism. Although the discriminant functions derived from the shape coordinate pairs correctly reallocated 81% of specimens to their sex, this value was not found to differ significantly from that of randomized data. The results of this study suggest that the consistency in patterns of between-population sexual dimorphism warrant caution when extrapolating from one sample to others for the purposes of sex discrimination.

Does Science Education Need the History of Science

This essay argues that science education can gain from close engagement with the history of science both in the training of prospective vocational scientists and in educating the broader public about the nature of science. First it shows how historicizing science in the classroom can improve the pedagogical experience of science students and might even help them turn into more effective professional practitioners of science. Then it examines how historians of science can support the scientific education of the general public at a time when debates over “intelligent design” are raising major questions over the kind of science that ought to be available to children in their school curricula. It concludes by considering further work that might be undertaken to show how history of science could be of more general educational interest and utility, well beyond the closed academic domains in which historians of science typically operate.

Variation in early hominin temporal bone morphology and its implications for species diversity

Temporal bone morphology features prominently in discussions of fossil hominin taxonomy and phylogeny. However, the complex morphology has led to different ways of interpreting features and, as a result, different conclusions regarding systematics. Here we use temporal bone anatomy and geometric morphometric techniques to ask how much disparity exists among early hominin temporal bones and whether levels of intra- and interspecific variation among fossil hominins are consistent with those among modern apes and humans. Using 3D ectocranial landmarks, Euclidean distances based on Procrustes coordinates were determined for all pairwise comparisons among 15 fossil specimens representing Australopithecus species and early Homo. These were then compared to distributions of intraspecific pairwise comparisons for five great ape and human samples, and interspecific comparisons for ten species pairs. Overlap between intra- and interspecific differences is pronounced in the extant as well as the fossil sample. On the whole, differences between fossil specimens matched the central tendency of differences between extant ape species or genera. In some cases the differences among fossils can also be found within highly variable extant species, even when the fossils are commonly recognised as different species. We conclude that the overall level of disparity among hominin specimens supports arguments that the clade is relatively speciose, but the pronounced overlap between intra- and interspecific variation suggests that classifications based largely on morphometrics would be unreliable.