An evolutionary paradox: Disease-driven social avoidance promotes cooperation while also increasing infection

Social interactions constitute the fundamental environment underlying both the evolution of cooperation and disease transmission. However, traditional research has largely treated these two processes as isolated systems, overlooking their potential interplay. In reality, when individuals can voluntarily choose to engage in social interactions, any change in social participation — triggered by either process — reshapes the contact network and creates a feedback loop, weaving the two processes into a tightly coupled coevolutionary system. In this work, we propose a coupled dynamics framework for the evolution of cooperation and disease transmission under voluntary participation, with two variant models. The results reveal a thought-provoking paradox: moderate, disease-driven social avoidance, while intuitively expected to suppress disease transmission, can unexpectedly lead to an expanded infection size while simultaneously enhancing the level of cooperation. This paradox arises due to the unique, highly mixed spatial distribution between cooperators and loners. Further analysis shows that this phenomenon is robust across a wide range of parameters but can be naturally alleviated when people’s sensitivity to perceiving the risk of disease transmission is sufficiently high. This study uncovers a subtle interplay between cooperation evolution and disease transmission in the real world, implying non-intuitive and potentially conflicting dynamics between cooperation and public health goals under certain conditions. Simultaneously, it highlights the importance of interdisciplinary joint modeling for understanding complex social systems.