Evolution of Fear and Social Rewards in Prey-Predator Relationship

Fear is a critical brain function that enables us to learn to avoid danger. While many researchers have argued that fear has evolved to escape predators, how varying predatory pressures have shaped fear and other rewards, including positive social rewards for collective grouping, remains an open question. In this study, we investigate the relationship between predatory pressure and fear using an evolutionary simulation of reinforcement learning (RL) agents, where prey and predator RL agents co-evolve their reward functions, including visual rewards for observing prey and predators. We found that fear-like negative visual rewards for predators evolved only when predators have larger visual rewards from their prey, making them more active in foraging. Furthermore, we found an interesting alternating branching of predator visual reward, which serves as an effective example of the emergence of fear.