My research focuses on the maintenance of phenotypic variation and the process of speciation in natural environments.

Together with my husband Peter Grant I have been studying Darwin’s finches on the Galápagos islands since 1973. Our work combines ecology and behavior with genetics and more recently genomics. Intensive fieldwork on Genovesa Island for ten years and on the small island of Daphne Major for 40 years has revealed how natural selection results in evolutionary change when finch populations are subjected to severe droughts and shortage of food. We have discovered how an exchange of genes through hybridization can lead to a collapse of two species into one under some circumstances, and to the formation of a new species under other conditions. Since these two island environments are entirely natural, never having been disturbed by humans, the study provides a model of evolution in contemporary time that helps to understand biological diversification over geological time. Some of the outstanding questions we are pursuing with our collaborators are concerned with the effects of introgressive hybridization on the underlying genetic composition of known changes in beak morphology and body size.