Merging morphological and genetic evidence to assess hybridization in Western Eurasian late Pleistocene hominins.

Previous scientific consensus saw human evolution as defined by adaptive differences (behavioural and/or biological) and the emergence of Homo sapiens as the ultimate replacement of non-modern groups by a modern, adaptively more competitive group. However, recent research has shown that the process underlying our origins was considerably more complex. While archaeological and fossil evidence suggests that behavioural complexity may not be confined to the modern human lineage, recent palaeogenomic work shows that gene flow between distinct lineages (for example, Neanderthals, Denisovans, early H. sapiens) occurred repeatedly in the late Pleistocene, probably contributing elements to our genetic make-up that might have been crucial to our success as a diverse, adaptable species. Following these advances, the prevailing human origins model has shifted from one of near-complete replacement to a more nuanced view of partial replacement with considerable reticulation. Here we provide a brief introduction to the current genetic evidence for hybridization among hominins, its prevalence in, and effects on, comparative mammal groups, and especially how it manifests in the skull. We then explore the degree to which cranial variation seen in the fossil record of late Pleistocene hominins from Western Eurasia corresponds with our current genetic and comparative data. We are especially interested in understanding the degree to which skeletal data can reflect admixture. Our findings indicate some correspondence between these different lines of evidence, flag individual fossils as possibly admixed, and suggest that different cranial regions may preserve hybridization signals differentially. We urge further studies of the phenotype to expand our ability to detect the ways in which migration, interaction and genetic exchange have shaped the human past, beyond what is currently visible with the lens of ancient DNA.

Mitochondrial DNA analysis reveals Plio-Pleistocene diversification within the chacma baboon.

Modern baboons evolved as a distinct lineage prior to 2.5 Mya. Previous scenarios of diversification within this lineage have assessed the phylogenetic position of the chacma baboon of southern Africa relative to other baboons, but have not examined variation within this taxon. Here we provide a phylogenetic analysis of lineage diversity across the range of the chacma baboon, and show that: (1) chacma baboons diverged as a separate lineage at approximately 1.84 Mya; (2) the chacma lineage is characterised by a deep lineage split dividing chacmas into northeastern (1.52 Mya) and southwestern (1.22 Mya) clades; (3) ruacana baboons of Namibia form their own distinct monophyletic group within the southwestern clade, emerging approximately 0.68 Mya. These patterns likely result from a complex interplay of genetic drift and gene flow as the chacma lineage diversified across a broad geographic landscape during the climatically variable Plio-Pleistocene.

Inferring Plio-Pleistocene southern African biochronology from facial affinities in Parapapio and other fossil papionins.

Buried in the same South African cave deposits as Australopithecus, fossil papionins have been referred to Parapapio (Pp. whitei, Pp. broomi, Pp. jonesi, Pp. antiquus), Papio (P. izodi, P. angusticeps, P. h. robinsoni), Theropithecus (e.g., T. darti), Gorgopithecus, or Dinopithecus on the basis of postcanine tooth size and descriptive morphology of the muzzle. The morphological patterns of variation that these papionins demonstrate can help to place the Australopithecus fossils into a biochronological context and provide valuable information for reconstructing regional Plio-Pleistocene turnover. To document these patterns of variation across fossil-bearing sites, we explore morphometric affinities within Parapapio, and between Parapapio and other Plio-Pleistocene taxa (Dinopithecus ingens, Papio angusticeps, Papio izodi, and Theropithecus darti) by analyzing a sample of interlandmark distances derived from 3-D coordinate data of the most complete fossil papionin specimens available. Bivariate and multivariate analyses show that Pp. whitei exhibits as much variation between sites and between individuals as Pp. broomi and Pp. whitei combined. Diversity in Parapapio at Makapansgat and Sterkfontein may suggest substantial time depth to the caves. Theropithecus darti, Dinopithecus ingens, Papio angusticeps, Pp. whitei from Bolt's Farm (BF 43), and Pp. jonesi from Sterkfontein (STS 565) differ considerably from one another. Other Parapapio specimens across sites form a separate cluster with P. izodi from Taung, suggesting a Pliocene age for this site.

Phenotypic covariance structure in tamarins (genus Saguinus): a comparison of variation patterns using matrix correlation and common principal component analysis.

Constancy of variation/covariation structure among populations is frequently assumed in order to measure the differential selective forces which have caused population differentiation through evolutionary time. Following Steppan ([1997] Evolution 51:571-594), this assumption is examined among closely related tamarin species (genus Saguinus), using two distinct approaches applied to the task of evaluating similarity in patterns of morphological variation: common principal component analysis and matrix correlations. While the results of these analyses may appear contradictory, closer examination reveals them as complementary, highlighting the wisdom of combined methodologies. Overall, the results reveal a close relationship among the morphologically based variance structures of the tamarin species a relationship whose pattern is consistent with the pattern of phylogenetic relatedness as found via a molecular genetic study. More specifically, both methodological approaches provide some support for divergence of S. geoffroyi and S. oedipus (with regards to their patterns of morphological variation) from other tamarin species. This suggests that variance/covariance structure may have diverged through evolutionary time in the tamarin lineage, placing assumptions of constancy in doubt.

Three-dimensional imaging in forensic anthropology: a test study using the Macintosh.

Forensic anthropologists have unique, albeit usually fleeting, access to modern skeletal remains. By constructing a database of three-dimensional images, such remains can be accessed long after the remains are gone. A method is proposed which uses Macintosh hardware and NIH Image software to preserve remains digitally through red-blue three-dimensional imaging techniques. Additionally, the qualitative and quantitative accuracy of these images is assessed. By creating this type of forensic database, anthropologists can address issues such as populational variance, thereby using modern forensic skeletal remains to explore some of the fundamental issues within anthropology.