Match the missing words in the following phrase. Darwin's finches developed different beak shapes and sizes on different islands. The original bird [A] that colonized the islands was genetically [B]. This meant that, although birds in the original population were [C], individual birds had slightly different beaks. Food sources differed between islands. Birds with beaks that were better suited to obtaining food on a particular island had [D] survival and reproduction rates, and the number of birds with suboptimal beaks [E] relative to the number of birds with well-suited beaks. Over evolutionary time, the beak shape became fixed in each [F].