Morphological Development at the Evolutionary Timescale: Robotic Developmental Evolution

Evolution and development operate at different timescales; generations for the one, a lifetime for the other. These two processes, the basis of much of life on earth, interact in many non-trivial ways, but their temporal hierarchy---evolution overarching development---is observed for all multicellular lifeforms. When designing robots however, this tenet lifts: it becomes---however natural---a design choice. We propose to inverse this temporal hierarchy and design a developmental process happening at the phylogenetic timescale. Over a classic evolutionary search aimed at finding good gaits for a tentacle robot, we add a developmental process over the robots' morphologies. In each generation, the morphology of the robots does not change. But from one generation to the next, the morphology develops. Much like we become bigger, stronger and heavier as we age, our robots are bigger, stronger and heavier with each passing generation. Our robots start with baby morphologies, and a few thousand generations later, end-up with adult ones. We show that this produces better and qualitatively different gaits than an evolutionary search with only adult robots, and that it prevents premature convergence by fostering exploration. This method is conceptually simple, and can be effective on small or large populations of robots, and intrinsic to the robot and its morphology, and thus not specific to the task and the fitness function it is evaluated on. Furthermore, by recasting the evolutionary search as a learning process, these results can be viewed in the context of developmental learning robotics.