Environmental variability promotes the evolution of cooperation among geographically dispersed groups on dynamic networks

The evolutionary process that led to the emergence of modern human behaviors during the Middle Stone Age in Africa remains enigmatic. While various hypotheses have been proposed, we offer a new perspective that integrates the variability selection hypothesis (VSH) with the evolution of cooperation among human groups. The VSH suggests that human adaptability to fluctuating environments was a primary force driving the development of key evolutionary traits. However, the mechanisms by which environmental variability (EV) influenced human evolution, particularly the emergence of large-scale and complex cooperative behaviors, are not yet fully understood. To explore the connection between intensified EV and the evolution of intergroup cooperation, we analyzed three stochastic models of EV: (i) Regional Variability (RV), where resource-rich areas shift while overall resource levels remain stable; (ii) Universal Variability (UV), where overall resource levels fluctuate but resource-rich areas remain stable; and (iii) Combined Variability (CV), where both resource-rich areas shift and overall resource levels fluctuate. Our results show that RV strongly promotes cooperation, while UV has a comparatively weaker effect. Additionally, our findings indicate that the coevolution of cooperation and network structures is crucial for EVs to effectively promote cooperation. This study proposes a novel causal link between EV and the evolution of cooperation, potentially setting a new direction for theoretical and empirical research in this field.Author summary: This study investigates how changing environmental conditions may have influenced the emergence of cooperative behaviors among early human groups during the Middle Stone Age in Africa, a pivotal period in human evolution. We present a novel approach to explaining the link between environmental changes and the evolution of cooperation by using models that simulate fluctuations in resource availability across various patterns. Our findings suggest that cooperation is more likely to emerge and sustain when resource distribution across regions varies over time, in contrast to cases where overall wealth changes but remains concentrated in fixed areas. Furthermore, our results indicate that the coevolution of cooperation and social structures is crucial in determining whether environmental changes foster cooperation, highlighting a dynamic interplay between environmental factors and social adaptability. We believe these findings contribute to broader discussions in anthropology, archaeology, and the study of complex systems, enriching our understanding of human nature and society.