Hybridization increases population variation during adaptive radiation

Significance Adaptive radiations, comprising many species derived from one or a small number of ancestral species in a geologically short time, are prominent components of the world’s biodiversity. Introgressive hybridization of divergent species has been important in increasing variation, leading to new morphologies and even new species, but how that happens throughout evolutionary history is not known. A long-term field study of Darwin’s finches on Daphne Major island, Galápagos, shows that introgression enhances variation and increases the potential for future evolution. We use a dated phylogeny to infer that populations became more variable in morphological traits through time, consistent with this enhancement effect, and then declined in variation after reaching a maximum. Introgression may be especially important with future climate change.