Doctoral Dissertations

Date of Award

5-1996

Degree Type

Dissertation

Degree Name

Doctor of Philosophy

Major

Anthropology

Major Professor

Fred H. Smith, Andrew Kramer

Committee Members

Andrew Kramer, Richard Jantz, Jan Simek, Mike McKinney

Abstract

Within the past several decades, the origin of modern humans has taken on renewed importance and has generated significant controversy in the world of human evolutionary studies. This debate has focused on discoveries in sub-Saharan Africa and new dating of fossil hominids, (e.g., St. Cesaire, Skhul and Qafzeh), as well as recent developments in the field of human genetics.

Recently four models of modern human origins have risen to the forefront of the debate. These are: (1) The Recent African Evolution Model (RAE), which proposes that early anatomically modern Homo sapiens appeared in sub-Saharan Africa approximately 200 ky BP as a result of a cladogenetic event. These modern humans radiated out of Africa, replacing the archaic human populations they encountered. (2) The Multiregional Evolution Hypothesis (MRE) which holds that the origins of modern humans took place in regional contexts throughout the Old World through a complex interaction of gene flow, drift and selection. In this model, cladogenesis does not occur. (3) The Afro- European sapiens Hypothesis, (AES) states that, while it is likely that modern humans did originate in sub-Saharan Africa, it is not likely that a complete replacement occurred, but that over a short time, the archaic human genome was replaced. This model postulates cladogenesis in the origin of modern humans with limited hybridization at zones of contact. (4) The Assimilation model, which holds that, while Africa may well have been the homeland of the earliest modern humans, considerable genetic exchange is thought to have taken place between moderns and archaics in combination with selection for newer, more modern genes. This model is non-cladogenetic.

While each of these models has attempted to understand the evolution of modern humans, none have addressed the question of what, exactly, a modern human is. It is only through understanding diversity in anatomically modern Homo sapiens that we can hope to separate that which is modern from that which is not. While various epistemologically-driven definitions of modern humans have been put forth, none have been effective in defining modern humans.

Looking at this problem from a different angle, I propose that, if the world-wide variability of known, recent modern human crania can be quantified, a metric definition of anatomically modern Homo sapiens can be derived. The question then becomes not what is a modern human, but at what time did hominids that conform to a modern human metric pattern appear in the fossil record. Given that such a definition can be derived, certain predictions can be made about which concept of species evolution best fits the fossil evidence, and, by extension, which of the current models of modern human origins is best supported.

Using Darroch and Mosimann's size adjustment technique, 98 fossils pertinent to the origins of modern humans are compared to a reference sample of 2354 known extant modern human crania to determine if they conform to a modern metric pattern. Statistical analysis involves the use of principal components and canonical discriminant analysis. Due to the fragmentary nature of the hominid sample, thirty separate analyses are performed involving different variable sets to encompass all of the fossils. A Mahalanobis distance is generated for each fossil per analysis from the modern human centroid. A fossil is said to be in the modern human range if it conforms to the 95% confidence interval of the modern sample. This is obtained by means of a chi-square table.

Additionally, a randomization test is performed in which the extant modern sample is broken up into four random groupings and distances generated. These distances are then compared to actual distances from regional centroids to determine if the earliest modern fossils have regional affinities,

The results of this study strongly suggest that for three areas of the Old World: Central Europe, Southwest Asia, and possibly East Asia, the appearance of a modern metric pattern was a gradual process. Data for the fourth and fifth areas, Australasia and Africa, are inconclusive. Furthermore, the earliest modern human fossils do not seem to show any regional affinities with the known, extant modern sample. These results indicate that the evolution of modern Homo sapiens did not involve a cladogenetic event but rather, was an anagenetic process in these regions. Further, the results do not unequivocally support the appearance of a modern metric pattern in sub-Saharan Africa before it appears in other regions.

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