Evolution of Fear and Social Rewards in Prey-Predator Relationship
This work addresses the complex interplay between fear and social rewards in evolutionary biology, providing insights into how environmental conditions shape innate behaviors, though it is incremental as it builds on existing simulation-based approaches.
The study tackled the evolution of fear and social rewards in prey-predator relationships using a distributed evolutionary simulation, finding that social reward is more critical for prey survival than fear-like negative reward, which only evolves after social reward is acquired, with fear emergence amplified by predators with larger mouths but more stable with non-evolving predators.
Fear is a critical brain function for detecting danger and learning to avoid specific stimuli that can lead to danger. While fear is believed to have evolved under pressure from predators, experimentally reproducing the evolution is challenging. To investigate the relationship between environmental conditions, the evolution of fear, and the evolution of other rewards, such as food reward and social reward, we developed a distributed evolutionary simulation. In our simulation, prey and predator agents co-evolve their innate reward functions, including a possibly fear-like term for observing predators, and learn behaviors via reinforcement learning. Surprisingly, our simulation revealed that social reward for observing the same species is more important for prey to survive, and fear-like negative reward for observing predators evolves only after acquiring social reward. We also found that the predator with increased hunting ability (larger mouth) amplified fear emergence, but also that fear evolution is more stable with non-evolving predators that are bad at chasing prey. Additionally, unlike for predators, we found that positive rewards evolve in opposition to fear for stationary threats, as areas with abundant leftover food develop around them. These findings suggest that fear and social reward have had a complex interplay with each other through evolution, along with the nature of predators and threats.