Evolution of Fear and Social Rewards in Prey-Predator Relationship

TL;DR

This study uses evolutionary simulations of reinforcement learning agents to explore how predatory pressures influence the development of fear and social rewards, revealing the roles of active predators and environmental factors in their evolution.

Contribution

It introduces an evolutionary simulation framework where prey and predator agents co-evolve their reward functions, uncovering how different environmental pressures shape fear and social reward evolution.

Findings

Fear-like negative rewards evolved in prey under predatory pressure.

Positive social rewards for grouping emerged in certain conditions.

Active predators, not static threats, significantly influenced fear evolution.

Abstract

Fear is a critical brain function that enables us to learn to avoid danger via reinforcement learning (RL). 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 RL agents with evolving rewards. In our simulation, prey and predator RL agents co-evolve their reward functions, including visual rewards for observing prey and predators. While fear-like negative visual rewards for predators often evolved in prey, we also observed cases in which positive rewards for both predators and prey evolved, the latter serving as a social reward for collective grouping. A comparison between different environmental conditions revealed that stronger predator hunting capability promoted stronger fear reward, while less food supply promoted more negative social reward. Moreover, fear did not evolve in response to static pitfalls with non-lethal damage, suggesting that actively hunting predators played an important role in its evolution. These results highlight the special role of predators in the diverse evolution of fear and social rewards.