Exploring the role of the tail in bipedal hopping through computational evolution

Abstract

Bipedal hopping has evolved as a mode of terrestrial locomotion in relatively few mammalian species. Despite large differences in body size, habitat use, and having evolved independently, all species that use bipedal hopping have remarkably similar limb morphology and posture. In addition, these species all have relatively long tails, presumably to assist in maintaining stability. However, the evolution of this behavior, and specifically the role of the tail, is not well understood. In this paper, we explore the evolution of bipedal hopping in a simulated animat, using a relatively simple musculoskeletal model and a rigid-body physics simulation environment. Results indicate that characteristically different hopping gaits evolve with alterations to the morphology, including 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 effective hopping evolved despite key differences from nature, potentially inspiring new design approaches in robotic and biomechanical systems.