Nervous System: Evolution in Relation to Behavior

Abstract

Animals' nervous systems are responsible for generating their myriad behaviors. All nervous systems are composed of broadly similar sets of molecular components (e.g., voltage-gated ion channels, G-protein coupled receptors, synapses) organized into neurons, neural circuits, and entire nervous systems. These may be diffused nerve nets containing hundreds of neurons, as in Cnidarians, or highly centralized and cephalized brains containing billions of neurons, as in some vertebrates. The evolution of these nervous systems has been influenced by selective pressures acting on their functional output (behavior), their developmental program, and their phylogenetic context. Improving behavioral performance to generate adaptive behavior requires greater spatial and temporal resolution of sensory, motor, and memory systems, but these improvements incur substantial energetic costs that penalize excess capacity. Therefore, there is a trade-off between behavioral performance and energy costs that influences all aspects of nervous system design. This trade-off combined with developmental and phylogenetic considerations can explain the very different anatomies, physiologies, and behavioral outputs of nervous systems.