Leonard Jenyns on the variation of species and Charles Darwin on the origin of species 1844–1860

The Reverend Leonard Jenyns (1800–1893) was an eminent naturalist who devoted much thought to the nature of species versus varieties (sub-species or ‘races’) in relation to sustained and heritable effects of environment and geography, and to questions about transmutation and the creation or other origins of progenitors. His lecture given in 1856 to the British Association for the Advancement of Science on ‘The variation of species’ summarized his thinking at this time and made recommendations for future research. Jenyns was a long-standing friend of Charles Darwin, both being influenced by J. S. Henslow as undergraduates at Cambridge, where they met. Jenyns was proposed by Henslow before Darwin as naturalist companion to sail on HMS Beagle , but he declined. Jenyns subsequently identified and catalogued fish collected on the voyage for Darwin, and they corresponded about natural history over many years. Darwin asked to read the full manuscript of Jenyns’ lecture, but not until 9 April 1858, shortly before receiving in June the letter from Wallace which accelerated his public disclosure of his theory of evolution. Here we transcribe Jenyns’ manuscript for the first time and discuss the implications of their similarities and differences of opinion at that critical time for evolutionary thinking.