The Beagle visited the Galápagos Islands, off the coast of Ecuador. There Darwin collected many specimens of birds, animals and plants and, while there, learned from the local people that they could identify the island from which a tortoise had come by its shell. In writing up his notes as he left the islands he observed that different species of mockingbird occurred on different islands.1
The detailed identification and publication of the birds was undertaken by John Gould, curator of the Zoological Society Museum in London 2,3 and this led to the discovery that different species of finch occurred on the different islands too.
These differences between species led Darwin to write at the time ‘such facts would undermine the stability of species’.4 In other words, perhaps these different species on the different islands had at one time been the same, before they were isolated from one another. He wrote later this ‘seemed to me to throw some light on the origin of species’. He started a notebook on the “Transmutation of Species” in 1837 and his first known evolutionary tree is depicted there.5
