The artifact-systems created by humans will be sure to generate deeper interactions with the surrounding natural world in the coming century. "System Life" seems to be a strong candidate as a leading paradigm which creates harmony in the world of natural entities and artifact-systems interacting each other, and solves any conflicts between human-machine interaction. This paper proposes a new concept named "Evolvable Exterior" as one of the essential elements that makes the "System Life" competence embody into artifact-systems.
We have been focusing on the predator-prey interactions as an origin of dynamics producing transition of color patterns. Predator-prey interactions can be considered one of the driving forces in evolution. Successful predation events characteristically follow a sequence of six stages -- encounter, detection, identification, approach, subjugation and consumption. Prey wish to interrupt this sequence as soon as possible by means of defences, whereas predators wish to reach the conclusion quickly by means of counter-defences. Predation and predator defence go back at least to the early Cambrian, so we can assume that prey have evolved many methods to terminate predation as early as possible. Among many means of defence and counter-defence, color patterns on their epidermis play an important role in the detection and identification stages. For example, some species match the color and pattern of the background to avoid detection by predators (crypsis), and some species bear special resemblance to inedible objects (masquerade) or distasteful species (mimicry). Therefore, the epidermis patterns of animals and plants are functional and dynamic in this context. At the same time, it is true that they constitute beautiful and harmonious scenes, as a result, and we feel comfortable in natural scenes.
Motivated by above-mentioned consideration, we have started investigating the feasibility of the evolution of color patterns on the surface of artifact-systems using the dynamics of predator-prey interactions observed in nature. This paper describes the concept of "Evolvable Exterior", and then reports our efforts to abstract the evolutionary mechanism of color pattern generation and color pattern recognition, and to construct a model in which coevolutionary dynamics automatically generate some of the color patterns that one observed in nature one after another. In the model, the world has several species among which there are predator-prey relationships (Fig. 1). Each organism has a pattern development system and a pattern recognition system. The pattern development system, which can be considered a two-dimensional extension of the 0L-system by Lindenmayer, has five generative grammars, which are passed on to offspring by genetic operations. One of the five grammars develops the color pattern on its epidermis. The other four grammars develop color patterns for recognizing its predators, its prey, its kin and the background, respectively, which are compared with the color patterns on the epidermis of the organisms it has encountered. Various transitions of color patterns have been observed in the experiments (Fig. 2). The epidermis patterns of organisms as prey have a tendency to become misleading patterns, for example, which are similar to the patterns for predators in the recognition systems of the predators. At the same time, the epidermis patterns of the organisms as predators also have a tendency to become misleading patterns, for example, which are similar to the patterns for prey in the recognition systems of the prey. Color patterns developed by the grammars for recognition, in general, follow the transitions of color patterns of prey, predators and kin, because the more similar the patterns are, the higher the organism's score. Coevolution requires a specific evolutionary response by both species: specific new defences by the prey must be continually counteracted by specific new defence-breakers in the predators and vice versa.
One of the ultimate goal of this approach is to realize dynamic transition of color patterns on the surface (display devices) of the artifact-systems based on the interactions among surrounding entities, while it is our present purpose to put this model into concrete shape as a design tool based on the results of the experiments.
References  T. Arita and A. Ojika, "Generation of Color Patterns Based on the Interactions between Predators and Prey", IEEE International Conference on Evolutionary Computation, pp. 291-294 (1996).