Date of Award

8-2006

Degree Type

Dissertation

Degree Name

Doctor of Philosophy

Major

Anthropology

Major Professor

Andrew Kramer

Committee Members

Lyle Konigsberg, Mohamed Mahfouz, Richard Jantz

Abstract

Theoretical adaptive landscapes and mathematical representations of key constraints of evolutionary and primate biology are used to propose a new hypothesis for the origin of hominid bipedalism. These constraints suggest that the selective pressure that produced this novel form of locomotion was the need for effective suspensory and terrestrial movement. This testable hypothesis, termed the Decoupling Hypothesis, posits that bipedalism is an adaptation that enables the shoulder to maintain a high degree of mobility, a feature important to suspensory behaviors, in the face of significant demands for a high degree of stability, a feature important for highly effective terrestrial quadrupedism.

Activity budgets and locomotor and postural behaviors of 18 primate groups, derived from published literature, were used to test a prediction of the Decoupling Hypothesis that bipedalism is a predictable behavior in primates which is correlated with intense demands for shoulder mobility and stability. Time was used as a proxy for estimating conflicting demands for shoulder stability and mobility. Bipedalism, as a proportion of all above-substrate locomotion, was predicted using logistic regression including seven linear variables and four two-way interaction terms. All possible regressions, using R2 and Mallow’s Cp as criterion, and stepwise variable selection procedures were used to determine significant variables.

The model with a relatively high R2 (0.86) and the lowest Mallow’s Cp (-1.62), contained the following predictor variables: shoulder-abduction locomotion (p < 0.0001), shoulder-abduction posture (p = 0.0003), and an interaction terms, shoulder-abduction locomotion by above-substrate locomotion (p = 0.011). The significant interaction term, predicted by the Decoupling Hypothesis, supports the hypothesis and suggests that further consideration is warranted.

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