Intellectual priority is often hard to establish (Letters 3 and 8 December). Evolution was very much "in the air" in the 1850s; the crucial question was "what is the mechanism?". (As it happened, both Darwin and Wallace found their inspiration in Malthus). Wallace's letter of 1858, succinctly setting out his mechanism, sent Darwin into a panic and we know that Charles Lyell and Joseph Hooker took the matter out of his hands and arranged that miscellaneous evidence of Darwin's priority, with the letter, would be presented at the Linnean Society. This was an untidy and unusual process, but I am not convinced the alleged conspiracy went further than that.
Thereafter Darwin fully acknowledged their discovery to have been a joint one and Wallace seemed happy throughout his long life to regard Darwin as the senior partner in the enterprise of Darwinism, the title of his own book on natural selection. Darwin was subsequently relieved to find that Wallace was an agreeable and generous man who harboured no resentment. The most likely reason for Wallace's subsequent demotion was probably his later pursuit (right up to 1913) of unpopular causes, including land nationalisation, socialism, spiritualism and anti-militarism.
Emeritus professor David Collard
University of Bath
• Charles Darwin did not have the theory of evolution as we now understand it 20 years before publishing On the Origin of Species. His migration theory of 1844 still dominated his thoughts until Hooker damned it unreservedly in the summer of 1856. Only in the months which followed did Darwin's ideas begin to resemble those published by Alfred Russel Wallace in September 1855, September 1856 and those received in a private letter in January 1857, but which Darwin only admitted receiving in a letter he dated 1 May 1857. All this is made clear in The Darwin Conspiracy by Roy Davies.
Professor Mark Brake
University of Glamorgan