PT - JOURNAL ARTICLE AU - Gáspár Jékely AU - Fred Keijzer AU - Peter Godfrey Smith TI - An Option Space for Early Neural Evolution AID - 10.1101/027425 DP - 2015 Jan 01 TA - bioRxiv PG - 027425 4099 - http://biorxiv.org/content/early/2015/09/28/027425.short 4100 - http://biorxiv.org/content/early/2015/09/28/027425.full AB - 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: behavior, 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.