Robotics is an applicative science, growing up from many different fields of knowledge, whose main goal is to build artefacts which move inside an environment in a way to remember the behaviour of some living system. Of course, industrial manipulators substituting human workers in a factory, are devoted to assembly components to manufacture final "products" to be sold on markets; nevertheless, their rapid movements can rensemble those of some flexuous animal. A more suggestive impression can be received observing an autonomous vehicle while is moving around or a legged-robot which is trying to emulate its living counterpart.
These very simple citations come from a wide literature about the current state of art involving robotics and its applications and they would demonstrate how strong is the influence of ethology and biology but also cognitive psychology and neurobiology.
However, the ancestor of robotics can be considered cybernetic with its theoretical studies on communication and control processes within systems, expecially, compared between artificial and biological ones. The well-known principle of feedback is considered the turning point to understand and synthetize features observed in both artificial and natural living systems.
So, the biological metaphor could be a good starting point to enter the fascinating world of robotics but it doesn't cover all the actual implementations found both in research laboratories and industrial assembled manufactures. A second motivation of this statement is originated by the early works in robotics which emphasized the prominence of the symbolic intelligence over the ability to take advantages from the limitations set by the environment.
Nevertheless, shading the light on the brains of robots rather than on their bodies, allows us to move the details of robot sensors and actuators towards the understanding the behaviours they exhibit in order to implement their control mechanisms which provide them with the requested behaviours. But the symbol system hypothesis has been dominating Artificial Intelligence for so a long time that the problem to provide a robot with a brain has been cast in what it's generally known as deliberative thinking paradigm.
Every intelligent activity is implemented as a reasoning process which operates on a symbolic internal model resulting in the sense-think-act when it is applied to autonomous robots. In these sense a planner, namely, the abstract controller of any robot operation, is a knowledge-based system which implements a hierarchical process that controls the order in which a sequence of operation is performed.
The behaviour-based approach, originated by the pioneristic work of Brooks in the 80' middle, has changed the perspective shifting the attention towards the notion of sensing and acting within the environment, rather than focusing on knowledge representation and planning. In this sense the subsumption architecture, first devised by Brooks implementing the robot Allen, has become synonimous of reactive system even if today this term is used with the meaning of behaviour-based system.
The biological and ethological motivations to implement such systems should be also considered expecially when adaptive behaviours are requested to operate in partially unknown environments. Recently, a large interest in collective robotics has come to maturity as a consequence of a growing demand for robust and reliable autonomous robots.