Revisiting evolution at the rear edge

Rear-edge populations occur at species' warmer range limits, with many still occupying glacial refugia. They offer insights into evolution under changing climates, yet they are underused as models. We identify three equally likely evolutionary patterns in rear edges: high genetic diversity and differentiation, elevated genetic drift, and strong local adaptation. Multiple patterns create challenges for predicting the vulnerability, conservation value, and adaptive potential of rear edges under future climates. Which factors drive these distinct outcomes, and why only some rear edges persist in former refugia, remains unclear. We propose to address these gaps by leveraging stable, receding, and trailing rear edges as evolutionary models of persistence and decline to improve predictions of species' responses to changing climates.