Human evolution

Human handedness is likely related to brain lateralization and major cognitive innovations in human evolution. Identifying handedness in the archaeological record is,
therefore, an important step in understanding our cognitive evolution. This thesis reports
on experiments in identifying knapper handedness in lithic debitage. I conducted a blind
study on flakes (n=631) from Acheulean handaxes replicated by right- and left-handed
flintknappers. Several flake characteristics significantly indicated handedness, with a
binary logistic regression correctly predicting handedness for 71.7% of the flakes.
However, other characteristics were not associated with handedness. This is a result of
personal knapping styles, as additional analyses show that individual knappers associate
with some attributes better than handedness does. Continued work on these methodologies will enable analysis of Paleolithic assemblages in the future, with the ultimate goal of tracking population-level hominid handedness rates through time and using them as a proxy for cognitive evolution and language acquisition.

Three dimensional morphometrics and analysis of surface depths and breadths are used to compare the proximal articular surface of the first metatarsal among and between Homo sapiens, Pan troglodytes, Gorilla, Hylobates, and Pongo. Casts of the fossils AL 333-54, STX 5017 and OH 8 are analyzed in light of the data gathered. Significant differences in morphology exist between these species; the most extreme morphologies exhibited are in Homo and Hylobates. While the OH 8 articular surface is essentially indistinguishable from Homo sapiens, AL 333-54 and STX 5017 show a mosaic of human-like and ape-like traits, which indicates the retention of the ability to abduct and rotate the hallux. The cast of AL 333-54 shows many similarities to Gorilla, while demonstrating many changes in line with Homo . The cast of STX 5017 retains a surface morphology much like Gorilla and Pan, with fewer similarities to Homo compared to AL 333-54.

The Paranthropus head is characterized by features traditionally thought to be related to heavy chewing. McCollum [Science 284 (1999) : 301-305] proposed that palatal thickening is a response to developmental integration between the mandibular ramus, oral and nasal functional matrices, and the vomer, which inserts onto the premaxilla in Paranthropus and causes the palate to thicken instead of rotate during vertical expansion. I tested whether palate thickness increases as a byproduct of differential increases in the sizes of the oral and nasal functional matrices compared to growth in the mandibular ramus. To do so, I collected 3D volume and landmark data from computed tomography (CT) scans of extant (Homo sapiens, Pan troglodytes, Gorilla gorilla, Pongo pygmaeus) and extinct taxa (Australopithecus and Paranthropus), and tested counterpart relationships for bones in the cranium using scaling analyses. Results suggest that developmental constraints related to growth counterpart relationships in the skulll are unlikely to affect palate thickness in the genus Paranthropus.

This study examined the topography of prefrontal molds of human endocasts using three-dimensional laser scanning and geographic information systems (GIS) in order to carry out intra-species comparisons. Overall brain topography can indicate when major reorganizational shifts in brain structure happened in our evolutionalry history, and these shifts may indicate major shifts in cognition and behavior. Endocasts are one of the sole sources of information about extinct hominin brains ; they reproduce details of the brain's external morphology. Analysis of endocast morphology has never been done using GIS methodology. The use of GIS helps to overcome previous obstacles in regards to endocast analysis. Since this methodology is new, this research focuses on only one species, Homo sapiens and the area of focus is narrowed to the frontal lobe, specifically Broca's cap. This area is associated with speech in humans and is therefore of evolutionary significance. The variability in lateralization of this feature was quantified.

The timing of skeletal growth spurts in modern humans is unique among mammals. In modern humans, peak growth occurs after puberty during the adolescent period, whereas large-bodied non-human primates exhibit an earlier juvenile growth spurt. Based on limited data, previous researchers have suggested that Neanderthals experienced a late, modern human-like adolescent growth spurt. In this study, I examined the timing of stature and facial growth spurts in Neanderthals to test the hypothesis that Neanderthals grew like modern humans. In order to assess the timing of Neanderthal growth spurts, I plotted a non-human primate regression estimate of age at puberty onto Neanderthal stature and mandibular velocity growth curves. The mandibular growth curve exhibits a discernible growth spurt after puberty, reminiscent of the modern human adolescent growth spurt. Future research on additional regions of the skeleton is necessary to further refine this estimate for the timing of Neanderthal growth spurts.