A prominent characteristic of human brains is that the left and right sides of the cerebral cortex are functionally asymmetric. Understanding this hemispheric asymmetry or laterality requires consideration of the manner in which it emerged over evolutionary time. The present article considers several issues that arise in constructing scenarios for the evolution of laterality, with special emphasis on computational advantages of separating processes that might be described as complementary into sufficiently distinct cortical areas so as to increase the extent to which those processes can occur efficiently without interfering with each other. Recent research with other species suggests that some forms of laterality are very old in evolutionary terms and the advantage to survival of segregating complementary processes is proposed to have been a primary factor in favoring lateralized solutions to complex computational problems. Despite the fact that laterality is quite old, human laterality differs in important ways from that of even our closest primate relatives. Consequently, the present article also considers how several important milestones in human evolution may have served the continued evolution of laterality into the pattern characteristic of contemporary humans and how the effect of those milestones may be intertwined with the development of hemispheric asymmetry within an individual from conception through adulthood.
Keywords: evolution, handedness, hemispheric asymmetry, laterality, ontogeny