Lukáš Friedl

Technical Note: The Effect of Midshaft Location on the Error Ranges of Femoral and Tibial Cross-sectional Parameters

In comparing long-bone cross-sectional geometric properties between individuals, percentages of bone length are often used to identify equivalent locations along the diaphysis. In fragmentary specimens where bone lengths cannot be measured, however, these locations must be estimated more indirectly. In this study, we examine the effect of inaccurately located femoral and tibial midshafts on estimation of geometric properties. The error ranges were compared on 30 femora and tibiae from the Eneolithic and Bronze Age. Cross-sections were obtained at each 1% interval from 60 to 40% of length using CT scans. Five percent of deviation from midshaft properties was used as the maximum acceptable error. Reliability was expressed by mean percentage differences, standard deviation of percentage differences, mean percentage absolute differences, limits of agreement, and mean accuracy range (MAR) (range within which mean deviation from true midshaft values was less than 5%). On average, tibial cortical area and femoral second moments of area are the least sensitive to positioning error, with mean accuracy ranges wide enough for practical application in fragmentary specimens (MAR = 40-130 mm). In contrast, tibial second moments of area are the most sensitive to error in midshaft location (MAR = 14-20 mm). Individuals present significant variation in morphology and thus in error ranges for different properties. For highly damaged fossil femora and tibiae we recommend carrying out additional tests to better establish specific errors associated with uncertain length estimates.

Hominoid humeral morphology: 3D morphometric analysis.

Variation in humeral morphology among hominoids has long been recognized in relation to both phylogeny and behavior. Here, we use 3D landmark data to analyze humeral shape among hominoids, including hylobatids (n = 37), Pongo (n = 33), Homo (n = 74), Pan (n = 55), and Gorilla (n = 45) to examine the relative influence of phylogenetic history vs. locomotor adaptation on humeral shape. Principal components analysis (PCA) of Procrustes shape data derived from 19 humeral type II or type III landmarks (Bookstein, 1991) for these taxa reveals the following: PC1, which primarily reflects the humeral torsion (or lack thereof) and relative diaphyseal and epiphyseal breadths, separates the relatively narrow-shafted, small articular dimensions and low humeral torsion Hylobates, and to a lesser extent, Pongo, humeri from those of the African hominoids. PC2, which largely contrasts shafts that are posteriorly convex (high PC2 scores) with antero-posteriorly straight humeral shafts (low PC2 scores) separates Homo, who tend to have A-P straighter shafts, from the more A-P bowed humeral shafts of the apes. These shape patterns suggest that the bowed shafts of Pan, Pongo, and Gorilla (and to a lesser extent, hylobatids) are due to the fact that in each of these taxa, the humerus is a weight-bearing bone, whereas the shafts of Homo are freed from locomotion. More subtle behavioral indicators are also elucidated, whereas cluster analyses (minimum spanning tree fit to a principal coordinates [PCO] plot and UPGMA dendrogram) reveal strong phylogenetic signals in the hominoid humerus as well.

Right for the Wrong Reasons: Reflections on Modern Human Origins in the Post-Neanderthal Genome Era

The sequencing of the Neanderthal genome answered once and for all the question of whether these hominins played a role in the origins of modern humans—they did, and a majority of humans alive today retain a small portion of Neanderthal genes. This finding rejects the strictest versions of the Recent African Origin model and has been celebrated by supporters of Multiregional Evolution (MRE). However, we argue that MRE can also be rejected and that other, intermediate, models of modern human origins better represent the means by which modern humans became the only extant human species. We argue this because we reject one of the major tenets of MRE: global gene flow that prevents cladogenesis from occurring. First, using reconstructions of Pleistocene hominin census size, we maintain that populations were neither large nor dense enough to result in such high levels of gene flow across the Old World. Second, we use mammalian divergence and hybridization data to show that the emergence of Homo is recent enough that member species of this genus were unlikely to have been reproductively isolated from each other, even in the absence of the high levels of global gene flow postulated by MRE supporters.

Applicability and limitations of sex assessment based on foramen magnum

Sex assessment of skeletal remains in the context of forensic investigation is one of the most important components when constructing biological profile of the deceased individual since it helps to significantly narrow down the number of potential victims. Therefore, the number of methods suitable to estimate sex should be as wide as possible, especially for cases of highly fragmented remains. This paper offers a classification method for sexing human remains based on an area around foramen magnum and tests other similar discriminatory functions published elsewhere on an independent sample from the circummediterranean region. We provide discriminant and logistic regression functions for several sets of variable combinations derived from head CT images. None of the functions performs reliably enough to be used in the forensic context. The same holds true for other discriminatory functions published in the literature. For most of the functions, the failure rate (its inability to successfully assign sex of an unknown individual) reaches 100%. Thus, despite the fact that foramen magnum is sexually dimorphic in most populations, its use in sexing cranial remains in the forensic context should be limited only to cases in which we know population affinity of unknown skeletal remains and can provide referential data from the same population to estimate sex.

Right for the Wrong Reasons

The sequencing of the Neanderthal genome answered once and for all the question of whether these hominins played a role in the origins of modern humans—they did, and a majority of humans alive today retain a small portion of Neanderthal genes. This finding rejects the strictest versions of the Recent African Origin model and has been celebrated by supporters of Multiregional Evolution (MRE). However, we argue that MRE can also be rejected and that other, intermediate, models of modern human origins better represent the means by which modern humans became the only extant human species. We argue this because we reject one of the major tenets of MRE: global gene flow that prevents cladogenesis from occurring. First, using reconstructions of Pleistocene hominin census size, we maintain that populations were neither large nor dense enough to result in such high levels of gene flow across the Old World. Second, we use mammalian divergence and hybridization data to show that the emergence of Homo is recent enough that member species of this genus were unlikely to have been reproductively isolated from each other, even in the absence of the high levels of global gene flow postulated by MRE supporters.