Galapagos finches. Historical artwork of the heads of Galapagos finches, made by Charles Darwin in his book 'A Naturalist's Voyage', London, 1889. These studies aided his theory of evolution. Darwin drew the conclusion that they all came from a common ancestor, but had diversified and evolved to adapt to local food supplies on the different islands. In his own words, 'Seeing this gradation and diversity of structure in one small, intimately related group of birds, one might really fancy that from an original paucity of birds in this archipelago, one species had been taken and modified for different ends.'