Publication Date

7-1-2010

Abstract

The human mandible and cranium are parts of an integrated cranial complex. These regions are also major components of the modular system, which comprises multiple semi-autonomous areas within the body. Integration and modularity express structure and function across various hierarchical levels of organization in the body and are thus definable as two non-exclusive ways of viewing somatic structure. What is integrated at one level may be a separable, modular unit at another. This dissertation statistically examines the interface between integration and modularity as partitioned through various hierarchical levels in the human skull, including the mandible. This examination is framed as a suggestion for new definitions of modularity, both through properties and attributes. Cranial integration is usually defined as the degree to which cranial elements or regions are integrated across the skull, and modularity is defined as areas of localized integration within the skull. Modules result from changing function through time in an evolutionary context, thus being definable as areas of functionally driven, localized integration. Modules are also heritable, possessing a higher degree of internal organization than non-modular regions. Therefore modules are heritable areas of the skull, definable by function, which are more integrated within themselves than non-modular regions. Under this view modules are inherited patterns of integration, whether genotypic or phenotypic, resulting in the hypothesis that modules are constrained regions of morphology which are resistant to change within a taxonomic level such as species but necessarily express change across species. This dissertation proposes the new definition of modularity through an examination of the patterned internal structure of modules in multiple groups of modern human skulls. Results presented in this dissertation suggest modularity as currently defined in biology lacks rigor. A testable, scientific definition of modularity can only be defined in the context of arguments which are driven by both attributes and properties. This dissertation attempts to show that modules represent areas of invariance to axes of population and sex, that the human mandible fails several key tests for being described as a module, and that modularity itself may be secondary to an even more fundamental, constrained pattern of development in the skull. Finally, it is shown dimensionality of measurements themselves (two-dimensional versus three-dimensional) is, in itself, a predictor for analysis of the shape of modules in the skull. Disregard of any of the above factors would ultimately prevent accomplishment of the goal of a robust definition of the human skull from a scientific perspective.

Keywords

Modularity, Cranial Integration

Document Type

Dissertation

Language

English

Level of Degree

Doctoral

Department Name

Anthropology

First Committee Member (Chair)

Joseph Powell

Second Committee Member

Ed Bedrick

Third Committee Member

Osbjourn Pearson

Fourth Committee Member

Jeff Froehlich

Fifth Committee Member

Michael W. Graves

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