Inception of Darwin's theory

The inception of Darwin's theory occurred during an intensively busy period which began when Charles Darwin returned from the survey voyage of the Beagle, with his reputation as a fossil collector and geologist already established. He was given an allowance from his father to become a gentleman naturalist rather than a clergyman, and his first tasks were to find suitable experts to describe his collections, write out his Journal and Remarks, and present papers on his findings to the Geological Society of London.

At Darwin's geological début, the anatomist Richard Owen's reports on the fossils showed that extinct species were related to current species in the same locality, and the ornithologist John Gould showed that bird specimens from the Galápagos Islands were of distinct species related to places, not just varieties. These points convinced Darwin that transmutation of species must be occurring, and in his Red Notebook he jotted down his first evolutionary ideas. He began specific transmutation notebooks with speculations on variation in offspring "to adapt & alter the race to changing world", and sketched an "irregularly branched" genealogical branching of a single evolutionary tree.

Animal observations of an orangutan at the zoo showed how human its expressions looked, confirming his thoughts from the Beagle voyage that there was little gulf between man and animals. He investigated animal breeding and found parallels to nature removing runts and keeping the fit, with farmers deliberately selecting breeding animals so that through "a thousand intermediate forms" their descendants were significantly changed. His speculations on instincts and mental traits suggested habits, beliefs and facial expressions having evolved, and considered the social implications. While this was his "prime hobby", he was struggling with an immense workload and began suffering from his illness. Having taken a break from work, his thoughts of marriage turned to his cousin Emma Wedgwood.

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