When Captain FitzRoy approached his friend George Peacock, then a Fellow of Trinity College, to suggest a Cambridge man who would be fit and willing to accompany him on HMS Beagle, Peacock thought first of John Stevens Henslow, and then of Leonard Jenyns, the vicar of Swaffham Bulbeck and Henslow's brother-in-law, who was nearly ten years older than Darwin. Both declined the offer, Henslow because he was a married man with a family, and Jenyns, after a day’s hesitation, largely on account of his parish responsibilities. Both men then agreed that Darwin ‘in all respects, would be a fit man to go’ and so ‘his name was at once sent up to Capt. Fitzroy, and the appointment confirmed’.
Jenyns had known Darwin since he was an undergraduate at Christ’s College, Cambridge, but despite their difference in age, their shared passion for natural history drew them together. Jenyns noted that in those early days Darwin was ‘a most zealous Entomologist, and attended but little – so far as I remember – to any other branch of Natural History’. The two went on joint excursions to collect insects in the Fens and in the woods around Bottisham Hall, near Jenyns’s home. Indeed a friendly rivalry developed such that Darwin’s delight in seeing his name in print for collecting a rare insect in 1829 was enhanced because he had got one over on Jenyns, who noted rather soberly that Darwin ‘made a number of successful captures I had never made myself, though a constant resident in the neighbourhood’. Some of the beetles that were collected by Darwin when he was an undergraduate are currently exhibited in the University Museum of Zoology, Cambridge.
Jenyns may have pondered on his decision about the Beagle voyage but it is clear that he was not jealous, remarking that ‘no better man could have been chosen for the purpose’, a testament ‘to the grasp his master mind had taken of Natural History in all its departments, and quite revolutionizing the whole science of Biology as then conceived’.
When Darwin returned from the voyage there was no-one available to describe the fish that he had collected. At Darwin’s request Jenyns took on the challenge, although it was not an easy one: at that time Jenyns had only worked on fish from the British Isles. He started from first principles and made detailed scientific measurements and descriptions of each new fish on his regular visits to Cambridge. He humorously commented that just the mention of Darwin’s name brought on a fishy smell.
This task was to be the most rigorous and exacting scientific work that Jenyns would ever undertake and culminated in the Fishes of the Zoology of the Voyage of the Beagle published between 1840 and 1842. The manuscript version of this survives together with many of these fish specimens in the University Museum of Zoology. This collection includes type and other specimens, which remain of lasting value for scientists.
After Darwin’s return from the voyage of the Beagle Jenyns saw him ‘only at intervals’ but they remained in regular correspondence. Darwin’s letters to Jenyns still survive in Bath, where Jenyns moved in 1850.
Richard Preece and Tim Sparks, Fauna Cantabrigiensis: The vertebrate and molluscan fauna of Cambridgeshire by the Rev. Leonard Jenyns (1800-1893): transcript and commentaries (The Ray Society). There is information on this book, Leonard Jenyns, and his notebooks and collections at the University Museum of Zoology Cambridge on the UMZC website.
There is now a memorial window to Leonard Jenyns in the church at Swaffham Bulbeck.