Development of Darwin's theory

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

A Mockingbird from Galápagos Islands

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.

Darwin’s Finches from Galápagos Islands showing different beak forms.

Darwin’s first evolutionary tree

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

Darwin suffered considerable illness and this kept him away from the public debates on his book The Origin of Species. The most notorious of these was at the Oxford meeting of the British Association for the Advancement of Science in 1860 where Thomas Huxley was the main protagonist for evolution with Samuel Wilberforce, Bishop of Oxford, opposing it. Both sides claimed victory and it was there that Thomas Huxley became known as “Darwin’s bulldog”. It also fell mainly to others to apply Darwin’s theory and the exhibits on the next page give some examples that followed during the next forty years.

It should be noted also that Darwin did not use the term “evolution” in Origins until the sixth edition of 1872. Also apart from a passing reference that "Light will be thrown on the origin of man" by his theory,⁶ he did not publish substantively on human evolution until 1871.⁷ But reviewers and debaters saw his work otherwise, one reviewer opining “If a monkey has become a man – what may not a man become?” ⁸ 

The Origin of Species was published at a time of considerable intellectual and religious challenge. In general terms the scientific community was divided between the naturalist clerics and a movement to professionalize science in which Thomas Huxley was a prime mover. The churches had seen a marked increase in evangelism only to be confronted with the German-led “higher criticism” which questioned traditional views on the authenticity and chronology of the Bible. This controversy reached a peak about 1860 in the Anglican Church and eclipsed the arguments over Darwin's newly published book.