Select image to enlarge Darwin famously commented that, 'in the thirteen species of ground-finches, a nearly perfect gradation may be traced from a beak extraordinarily thick to one so fine that it may be compared with that of a warbler. I very much suspect that certain members of the series are confined to different islands.' Darwin went on to add, '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.'

The Interactive Fly resides on the
Society for Developmental Biology's Web server.