Exploring the Role of the Tail in Bipedal Hopping through Computational Evolution

Abstract

Bipedal hopping has evolved as a mode of terrestrial loco-motion in relatively few mammalian species. Despite large differences in body size, habitat use, and having evolved in-dependently, all species that use bipedal hopping have re-markably similar limb morphology and posture. In addition, these species all have relatively long tails, presumably to as-sist in maintaining stability. However, the evolution of this behavior, and specifically the role of the tail, is not well un-derstood. In this paper, we explore the evolution of bipedal hopping in a simulated animat, using a relatively simple mus-culoskeletal model and a rigid-body physics simulation en-vironment. Results indicate that characteristically different hopping gaits evolve with alterations to the morphology, in-cluding the structure and actuation of the tail. Many of the the results are consistent with behaviors and morphologies observed in natural organisms. However, in some cases ef-fective hopping evolved despite key differences from nature, potentially inspiring new design approaches in robotic and biomechanical systems.