MOVEMENT IS A fundamental characteristic of living systems (see Figure 1). Plants and animals must move to survive. Animals are distinguished from plants in that they have to explore the world to feed. The carnivorous plant remains at a fixed position to catch the imprudent insect. Plants must make use of self-centered motions. At the same time the cheetah goes out looking for food. Feeding is a paragon of action. Any action in the physical world requires self-centered movements, exploration movements, or a combination of both. By analogy, a manipulator robot makes use of self-centered motions, a mobile robot moves to explore the world, and a humanoid robot combines both types of motions.