Mechanism of Emergent Symmetry Properties on Evolutionary Robotic System

In order to create an autonomous robot with the ability to dynamically adapt to a changing environment, many researchers have studied robotic intelligence, especially control systems, based on biological systems such as neural networks (NNs), reinforcement learning (RL), and genetic algorithms (GA) (Harvey et al., 1993, Richard, 1989, and Holland, 1975). In a recent decade, however, it has been recognized that it is important to design not only robotic intelligence but also a structure that depends on the environment as it changes because the dynamics of the structural system exerts a strong influence on the control system (Pfeifer & Scheier, 1999, and Hara & Pfeifer, 2003). The behavior of a robot is strongly affected by the physical interactions between its somatic structure and the outside world, such as collisions or frictions. Additionally, since the control system, the main part of robotic intelligence, is described as a mapping from sensor inputs to actuator outputs, the physical location of the sensors and actuators and the manner of their interaction are also critical factors for the entire robotic system. Therefore, to design a reasonable robot, it is necessary to consider the relationship between the structural system and the control system, as exemplified by the evolution of living creatures. From this point of view, several researchers have tried to dynamically design structural systems together with control systems. Sims (Sims, 1994) and Ventrella (Ventrella, 1994) have demonstrated the evolution of a robot with a reconfigurable multibody structure and control system through computer simulation. The Golem Project of Lipson and Pollack has realized the automatic design and manufacture of robotic life forms using rapid prototyping technology (Lipson & Pollack, 2000). Salomon and Lichtensteiger have simulated the evolution of an artificial compound eye as a control system by using NNs and have shown that the robot creates motion parallax to estimate the critical distance to obstacles by modifying the angular positions of the individual light sensors within the compound eye (Salomon & Lichtensteiger, 2000). These researches have shown the importance of adaptation through not only intelligence but also the relationship between morphology and intelligence. However, the mechanism of the function emerging from such relationship or some kind of design principle is not fully understood yet. Meanwhile, for living creatures, symmetry properties may be a common design principle; these properties may have two phases, that is, the structural and functional phases. For