How the Morphology Encoding Influences the Learning Ability in Body-Brain Co-Optimization

Embedding the learning of controllers within the evolution of morphologies has emerged as an effective strategy for the cooptimization of agents' bodies and brains. Intuitively, that is how nature shaped animal life on Earth. Still, the design of such cooptimization is a complex endeavor; one issue is the choice of the genetic encoding for the morphology. Such choice can be crucial for the effectiveness of learning, i.e., how fast and to what degree agents adapt, through learning, during their life. Here we evolve the morphologies of voxel-based soft agents with two different encodings, direct and indirect while learning the controllers with reinforcement learning. We experiment with three tasks, ranging from cave crawling to beam toppling, and study how the encoding influences the learning outcome. Our results show that the direct encoding corresponds to increased ability to learn, mostly in terms of learning speed. The same is not always true for the indirect one. We link these results to different shades of the Baldwin effect, consisting of morphologies being selected for increasing an agent's ability to learn during its lifetime.