A simulation study on the evolution of hopping motions in animals

This work was designed to investigate biomechanical aspects of the evolution based on the hypothesis of dynamic cooperative interactions between the locomotion pattern and the body shape in the quadrupedal hopping and the bipedal hopping. The musculoskeletal sagittal-plane model used in the computer simulation consisted of several segments; foot, shank, thigh, trunk, forearm, upper arm, and tail. Two adjacent segments were connected by a hinge joint, and each joint angle was controlled by an extensor and a flexor muscle. The nervous system was represented by a rhythm pattern generator which consisted of 12 neuron models. The genetic algorithm was employed based on the natural selection theory to represent the evolutionary mechanism. The simulation results showed that although hopping could not be seen in the early evolution process, repeated manipulations of the selection and multiplication increased the step length and the locomotion speed and that the resulting hopping motion was close to that of living animals. It was suggested that the advantage of the quadrupedal hopping is high energy efficiency and that of the bipedal hopping is high stability due to the simple and easy motion control. The computational evolution method employed in this study can be a new powerful tool for investigation of the evolution process mostly due to its versatility.