Brain Development and Evolution

This chapter reviews the development of the human brain from conception to adult age and its evolution across time and species. The size and the shapes of the various portions of the mature nervous system result from a variety of developmental processes such as cellular proliferation, cellular migration, and cell death, and also from the constraints imposed by the surrounding non-neural tissues. During brain development, neurons are dependent on external factors for guidance and survival. These factors include biochemical influences such as neurotransmitters and steroid hormones. The mechanisms involved are complex and require appropriate spatiotemporal relationships and feedback loops. Human brains appear to be products of evolutionary mechanisms such as selection and genetic variation. During the evolution of the nervous system, certain general trends seem to have occurred. Laterality in the cortex of humans represents a behavioral and morphologic reorganization within the brain.