Origin and Evolution of Nervous Systems

Abstract

Nervous systems integrate environmental and internal inputs to coordinate appropriate sometimes systems-level responses. Complex central nervous systems containing a brain and nerve cord(s) gained cognition, effectively forever changing the way in which organisms interact and adapt to their environment. How did such an incredible organ evolve? Classical views argue nervous systems and later centralization each occurred once in animal evolution, but over the last 15–20 years, rapid advances in molecular and genetic approaches as well as studies in a broader number of species provide surprising insights that force us to revisit the origin and evolution of nervous systems. In addition to causing biologists to reassess previous dogma, modern approaches provide a path forward to better address the age-old question: where did our brain come from? This chapter reviews our understanding of nervous system evolution through the lens of developmental biology. We focus on the emerging ideas that nervous systems may have evolved multiple times in animal evolution and revisit the evidence that argues centralization of nervous systems evolved once. We conclude with a brief discussion about the insights that can be gained by applying modern approaches in developmental biology to understand nervous system evolution.