According to the phrenological doctrine, as elaborated by Franz Joseph Gall, the shape of the skull reflects the `organs’ or faculties of the brain.
Phrenology attained considerable popularity in England: by 1832 there were 29 phrenological societies and an influential journal edited by George Combe.
Yet the theory is almost never mentioned by Darwin, who did not discuss it, nor mentioned in any of the two editions of the Descent of Man the experiments which by then had demonstrated that some movements hitherto attributed to free will could be produced by localised electrical simulation of the brain - (although a section on the brain was added to the second edition in 1874).
Darwin’s early doubts about one of the most popular Nineteenth-century theories of nature can be found in the correspondence: In 1830, a young Charles wrote to his cousin and friend William Darwin Fox “I forgot to mention, I dined with Sir J. Mackintosh & had some talk with him about Phrenology, & he has entirely battered down the very little belief of it that I picked up at Osmaston.”
Darwin had spent three weeks with Fox at Osmaston Hall, the Fox Family’s home, in the summer of 1829. Sir James Mackintosh (1765-1832) was a philosopher and historian who had studied medicine at Edinburgh; he and Josiah Wedgwood of Maer married two of the Allen sisters, so there was connection by marriage between the families. Darwin wrote about fist meeting Mackintosh during one of his visits to Maer in 1827 and later referred to him as `the best converser I ever listened to’ (The autobiography of Charles Darwin, p. 55)
Charles’ letter to Fox is both interesting in showing how a popular subject such as phrenology could be “picked up” or not, by young minds, but also how easily a conversation was enough to “batter down” any belief in it !