An option space for early neural evolution

Abstract

The origin of nervous systems has traditionally been discussed within two conceptual frameworks. Input-output models stress the sensory-motor aspects of nervous systems, while internal coordination models emphasize the role of nervous systems in coordinating multicellular activity, especially muscle-based motility. Here we consider both frameworks and apply them to describe aspects of each of three main groups of phenomena that nervous systems control: behaviour, physiology and development. We argue that both frameworks and all three aspects of nervous system function need to be considered for a comprehensive discussion of nervous system origins. This broad mapping of the option space enables an overview of the many influences and constraints that may have played a role in the evolution of the first nervous systems.

Keywords: cnidarian; ctenophore; nervous system evolution; peristalsis; phototaxis; sponge.

Figure 1.

Schematic of input–output and internal coordination systems. (Online version in colour.)

Figure 2.

Examples of input–output and internal coordination systems for the control of behaviour, physiology and development. (Online version in colour.)