Comparative Cognitive Development and Endocrinology in Pan and Homo
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CitationWobber, Victoria Elizabeth. 2012. Comparative Cognitive Development and Endocrinology in Pan and Homo. Doctoral dissertation, Harvard University.
AbstractKey insights into the evolutionary origins of human social behavior can be gained via study of our closest living relatives, bonobos (Pan paniscus) and chimpanzees (Pan troglodytes). Despite being equally related to humans, these two species differ importantly in aspects of their morphology, physiology, behavior, and cognition. Morphological comparisons reveal numerous traits in bonobos that can be viewed as paedomorphic, or juvenile, relative to chimpanzees. Meanwhile, comparisons of endocrinology in the two species suggest that aspects of steroid physiology have changed significantly in bonobos in line with their reductions in male mating competition. Based on this evidence, I tested the hypothesis that behavioral and cognitive differences between bonobos and chimpanzees derive from changes in their 1) developmental trajectories of behavioral and cognitive traits and 2) neuroendocrine influences on behavior and cognition. I tested this hypothesis by studying semi free-ranging populations of bonobos and chimpanzees. First, I found that bonobos retained juvenile levels of food sharing and social inhibition into adulthood, leading them to differ from chimpanzees in these traits as adults. Second, I found that bonobos showed muted elevations in their levels of testosterone from infancy to adulthood in comparison to chimpanzees, suggesting that numerous aspects of development differ between these two species. Third, I found that male bonobos and chimpanzees differ in their immediate neuroendocrine shifts surrounding competition, implicating changes in proximate mechanisms influencing social behavior between the two species. Fourth, I found that patterns of cognitive development in these two apes differed significantly from those of human children. These results provide substantial support for my hypothesis that phenotypic differences between bonobos and chimpanzees evolved via shifts in bonobo development and neuroendocrine physiology. More broadly, they illustrate how behavioral and cognitive evolution can occur through changes in ontogenetic trajectories and neuroendocrine mechanisms. These findings thus show the merits of integrating ultimate and proximate levels of analysis in studies of the evolution of human behavior and cognition.
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