Evolution photos
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Whitebark pine cone 
Seeds of whitebark pines (Pinus albicaulis) in California are dispersed by clark's nutcrackers. The cones produce sap, which is no problem for the nutcracker bird but keeps squirrels out. This reflects the evolution of a specialized relationship between birds and pines. Lassen Volcanic National Park, California. Photograph by Stanley A. Rice. Appears in Life of Earth (Prometheus Books).