Input from the External Environment and Input from within the Body

Behaviour responds to both input from the external environment and input from within the organism's body. Input from the external environment has mainly the function to regulate the execution of the organism's activities while input from the body is used to decide which activity to execute. We evolve artificial organisms which to survive and reproduce have to both eat food and drink water in equivalent quantities and therefore at any given time they have to decide whether to look for food or water. We show that in some environments the appropriate behaviour can evolve with no need for the organism's brain to know the current level of energy and water in the body while in other environments the brain needs this information from the body in the form of hunger and thirst. We discuss how the body and the body's interactions with the brain are part of the overall adaptive pattern of an organism and must co-evolve with brain and behaviour.