“An Inexplicable Confusion”

While visiting Galápagos, the young Charles Darwin was confused by the similarity of various finches he observed. We now understand that what we see as different finch species are “species before speciation is complete.” The confusion is inherent: many of them remain similar enough to form fertile hybrids. But a robust difference exists between the groups of ground finches and tree finches, raising the question, what prompted the evolution of that clear distinction? The primary habitats for tree finches are tree species of the wonderful Galápagos daisy genus, Scalesia, that dominate the forests of the humid areas of various islands. Did the evolution of daisies into trees influence the evolution of differences between ground and tree finches? For that matter, how did highland trees evolve from lowland shrubby daisies, thus forming the highland habitat for tree finches? Several lines of evidence, including a contemporary interaction analysis of various birds and trees, suggest that the giant daisies of Galápagos and the tree species of Darwin’s finches coevolved.