Human Adaptation to Risky Environments

Abstract

Local adaptation describes the process by which organisms develop specialized traits suited to their specific environment. In biological terms, this relationship is captured by the fundamental equation P = G + E + (G × E), where phenotype (P) represents observable characteristics emerging from dynamic interactions between genetic factors (G) and environmental influences (E). Like plants and animals, humans can develop local adaptations to particular environments, reflected in perceptual frameworks, behavioural patterns, and genetical characteristics. However, scientific evidence for local adaptation in humans remains relatively limited and underreported in the scientific literature. This study investigates human adaptation to an active volcanic environment, where generations persist despite catastrophic risk. Applying this biological framework, the research examines adaptation at the cognitive, behavioural, and genetic levels on the slopes of Mount Semeru (East Java, Indonesia). Through a large scale lab-in-the-field experiment within this natural laboratory of recurrent volcanic risk, and by exploiting an unexpected major eruption that occurred during data collection, we compared communities in the high-risk zone with those in relatively safer areas. Our findings show that chronic exposure to volcanic hazard shapes a unique adaptive perception. Residents in the high-risk zones perceive tangible and intangible benefits that offset objective threat. This context-specific rationale forms a foundational adaptive phenotype that overrides baseline demographic differences such as gender. This study also finds that long-term exposure shapes a stable behavioural phenotype of increased individual risk aversion, while socio-cultural norms such gotong-royong (mutual assistance) maintain stable prosocial tendencies. The 2021 Semeru eruption acted as a temporary catalyst, triggering a surge in solidarity without altering this underlying caution. This pattern demonstrates a dual adaptive strategy, where persistent hazard shapes personal caution, while sudden catastrophe triggers collective solidarity. Genetic analysis of the DRD4 gene, associated with novelty seeking, reveals a more complex picture. Although allele frequency differences were observed between zones, this genetic variation was not directly linked to financial risk taking in experiments. Instead, factor such as gender, age, number of children, and temporal context relative to the eruption showed significant associations. This suggest that the well-documented risk aversion among high-risk zone residents is not driven by simple genetic determinism. Overall, our study demonstrates that human persistence in extreme environments is built through integrated multi-level adaptation. A uniquely calibrated perception of the landscape enables habitation, which translates into a chronic personal caution phenotype, while deeply rooted cultural norms like gotong royong ensure stable prosociality and enable a strong, flexible response to acute crises. Together, these cognitive, behavioural, and cultural layers, interacting with a complex genetic basis, constitute a comprehensive model of human resilience on an active volcano.