The Evolution of Hemispheric Specialization in Primates

Hemispheric specialization, and lateralized sensory, cognitive or motor function of the left and right halves of the brain, commonly manifests in humans as right-handedness and left hemisphere specialization of language functions. Historically, this has been considered a hallmark of, and unique to, human evolution. Some theories propose that human right-handedness evolved in the context of language and speech while others that it was a product of the increasing motor demands associated with feeding or tool-use. In the past 20-25 years, there has been a plethora of research in animals on the topic of whether population-level asymmetries in behavioral processes or neuro-anatomical structures exist in animals, notably primates and people have begun to question the historical assumptions that hemispheric specialization is unique to humans. This book brings together various summary chapters on the expression of behavioral and neuro-anatomical asymmetries in primates. Several chapters summarize entire families of primates while others focus on genetic and non-genetic models of handedness in humans and how they can be tested in non-human primates. In addition, it makes explicit links between various theoretical models of the development of handedness in humans with the observed patterns of results in non-human primates. A second emphasis is on comparative studies of handedness in primates. There is now enough data in the literature across different species to present an evolutionary tree for the emergence of handedness (and perhaps other aspects of hemispheric specialization, such as neuro-anatomical asymmetries) and its relation to specific morphological and ecological adaptations in various primate species.