Doctoral Dissertations

Tal Simmons

Date of Award

8-1990

Degree Type

Dissertation

Degree Name

Doctor of Philosophy

Major

Anthropology

Major Professor

Fred H. Smith

Committee Members

Jan Simek, Richard Jantz, Michael McKinney

Abstract

This dissertation examines and evaluates models of modern human origins through an analysis of frontal bone morphology in Middle and Late Pleistocene fossil hominids from Africa, southwest Asia, and Europe. Many models have been proposed to explain the emergence of the anatomically modern morphotype in Homo sapiens; these models emphasize a variety of evolutionary processes in the hominid lineage, including speciation, selection, migration, replacement, and gene flow. The Out of Africa and Regional Continuity models, both of which address this phenomenon, are discussed with an emphasis on their underlying theoretical foundations in more basic evolutionary schematics. The former model is derived from the Punctuated Equilibrium Theory of Evolution, while the latter is grounded in the Synthetic Theory of Evolution. The fundamental components of these evolutionary theories operate as the constraints which govern both the structure of the two models and the implications which result from the application of those theories to the question of modern human origins. Relationships among Upper Pleistocene hominids of southwest Asia, Africa, and Europe are examined through a multivariate analysis of the frontal bone. A total of eighty-three fossil hominids compose the sample of frontal squama and browridge morphology data. Variables were log-transformed and included in Principal Components Analyses which enabled the evaluation of morphological similarity and biological relationships among these hominids. Scale-free "shape" variables were created in order to standardize the effects of residual size and reduce its influence. The resultant variables were also examined in Principal Components Analyses which allowed for the isolation of aspects of shape in the morphology of the frontal squama and browridge and an assessment of their relative importance to frontal morphology and population relationships. The importance of shape in considerations of both browridge thickness and frontal elevation is emphasized by the analysis. Regional specific patterns of browridge shape (non-size-correlated) and reduction of the browridge were significant and hence indicative of unique biological relationships among hominids that are unrelated to simple allometric variation (i.e irrespective of their overall size). The analyses were examined with regard to specific predictions which support either the Regional Continuity or Out of Africa models of modern human origins. The existence of a morphometrically transitional group between such forms as Kabwe and Saldanha and anatomically modern Homo sapiens was demonstrated for African hominids; this represented the only prediction of the Out of Africa model which was unequivocally supported by the data in these analyses. Also, the position of the Zuttiyeh specimen within the Neandertal archaic group, distinct in form from both the African transitional group as well as from the anatomically modern Skhul/Qafzeh hominids was substantiated. The north African archaic hominids are shown to exhibit similarities in browridge shape and pattern of reduction to the Levantine archaic group; whereas, the Shanidar Neandertals remain separate with regard to frontal shape morphology, thus lending support to previous indications of deformation. There is significant geographic patterning suggested by the analysis in addition to the separation of distinct archaic and modern morphotypes. Some geographic overlap is indicated, however, and may be related to the effects of gene flow and migration. The most significant prediction of the Out of Africa model - that the earliest anatomically modern humans in regions external to Africa should resemble the anatomically modern hominids from southern Africa more than they resemble locally indigenous populations of archaic humans - is not supported by the results of these analyses. Rather, there appears to be a considerable degree of continuity between archaic and modern Homo sapiens populations in non-African regions of the Old World. The migration of anatomically modern humans Out of Africa is seen to have acted as a catalyst for the development of modern humans in other regions, most significantly in the reduction of robusticity and overall size. The regional Continuity model is demonstrated to best explain the data analyzed in this study. Fossils which resulted from the contact between migrating anatomically modern human populations and indigenous archaic human populations exhibit mosaic characteristics of frontal bone morphology which are indicative of phylogenetic relationships to both hominid types. Indigenous populations of archaic humans contributed in qualitatively significant ways to the genetic variability of modern human populations.

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