January 30, 2012

AAPA 2012 abstracts (Part 3)

Continuing from Part 2.

An analysis of the Klasies River hominins using a hybrid model.
LILY MALEKFAR. Anthropology, Northern Illinois University.
Current research indicates that modern Homo sapiens originated in East Africa and then migrated across Africa as well as out of Africa, where they encountered archaic hominins. The Klasies River Main site (KRM) in South Africa is one location where there is evidence that modern and archaic Homo sapiens may have interacted. As Smith and other researchers have suggested, the KRM mandibular sample, in particular, exhibits significant size and morphological variability, which counters claims that the KRM specimens are fully modern.
The null hypothesis predicts that KRM’s range of variation does not significantly differ from the ranges of variation indicated in the comparative samples, including Sima de los Huesos, Krapina, Skhul, Qafzeh, and the Northern Illinois University (NIU) Collection, the latter containing specimens classified as modern Homo sapiens from India. If the null hypothesis is rejected, this would be tentative support that the KRM sample may possibly be a hybrid sample. This study examines first and second mandibular molar lengths and widths as well as mandibular corpus height and breadth in adult hominins and compares patterns of variation using the coefficient of variation.
The results demonstrate that the KRM sample is markedly more variable than any of the comparative samples, which rejects the null hypothesis and is one possible indicator of an admixed sample at KRM. This study is limited by small sample sizes for KRM. This and the fact that KRM spans several thousand years may impact these results.

The origins of dental modernity.
Research over the past decade has established that the study of dental morphological characters is a useful and important tool for interpreting the later stages of human evolution. A good deal of this research has focused on identifying dental characters that are relevant specifically to the distinction between Neandertals and H. sapiens, and more broadly to the question of modern human origins. However, while the dental patterns of certain recent H. sapiens populations have been described as primitive (e.g., Sub-Saharan Africans) or derived (Northeast Asians) relative to other groups, no study to date has proposed a dental pattern that characterizes H. sapiens as a species. To this end, this study investigates (1) whether or not there is a unique dental pattern in H. sapiens; (2) if so, which traits comprise this pattern; and (3) when, during the course of human evolution, these traits emerge. Our results show that size notwithstanding, H. sapiens has few uniquely derived dental traits that distinguish them from other hominins. These include the U-shaped fissure pattern of the lower P4, relatively flat, featureless upper incisors that are buccolingually narrow, lower molars lacking a hypoconulid and lower molars lacking any form of trigonid crest on enamel and dentine surfaces. Early H. sapiens from Qafzeh, Klasies River Mouth and Jebel Irhoud possess some of these characters. Interestingly, none of the recently discovered teeth from Qesem Cave, Israel exhibit any derived H. sapiens non-metric traits, while the molars of H. floresiensis are derived toward the H. sapiens condition.
Endocranial shape in early modern humans.
Humans have more globular brains and therefore endocasts than our extant and extinct relatives: chimpanzees and Neanderthals both have anterioposteriorly elongated endocasts. Based on an ontogenetic series of recent modern humans, we have previously shown that this modern human globular shape develops directly after birth during an ontogenetic phase that is absent in chimpanzees and Neanderthals. However, it is unclear at which point in the evolution of our species this unique pattern of brain development appeared.
Here, we aim to trace its evolutionary origin. Based on the shape of fossil adult humans, we investigate the morphological evolution of Homo sapiens endocasts using geometric morphometrics. Investigating representatives of H. sapiens from different time periods (comprising samples from Jebel Irhoud, Qafzeh, Skhul, Mladec, Cro-Magnon) makes it possible to assess when and how (gradually or rapidly) this developmental phase appeared in the course of recent human evolution. As several relevant fossils are fragmentary and partly deformed, they require reconstruction before they can be analyzed. To this end, we generate and reconstruct virtual endocasts based on CT scans. We first use mirror-imaging and segmentation techniques, and then the thin-plate-spline interpolation function for reference-based reconstruction. Generating multiple reconstructions based on landmarks of 60 recent human endocasts, we keep track of the reconstruction uncertainty throughout the shape analysis. We document temporal trends of endocranial shape within anatomically modern humans during the Late Pleistocene and discuss potential implications for the evolution of the modern human brain.


terryt said...

"The results demonstrate that the KRM sample is markedly more variable than any of the comparative samples, which rejects the null hypothesis and is one possible indicator of an admixed sample at KRM".

I'd be very surprised if it cannot be shown at some point that all human populations are a product of admixture. From my reading I am even sure that Australopithecus is a product of hybridism. In fact that seems to be how evolution works. A species expands geographically and each region produces its own genetic variations. Some of these variations prove advantageous to the species as a whole and they subsequently spread through it, or much of it. One of my friends calls it 'the wave theory of evolution'. Advantageous genes move through a species in the form of waves. The idea that any new species arises from the expansion of some previously isolated single group is very difficult to accept. My belief is that it is a product of the combination of deeply-ingrained biblical myths and the Industrial Revolution's economic idea of 'superiority' through survival of the fittest.

sykes.1 said...

Considering these and other results, what is the status of the Dobhzansky/Mayr species concept. It has been implicitly rejected by conservation biologists (red wolf, gray wolf, timber wolf...), do anthropologists still accept it?