John Stevens Henslow (1796–1861)

The letter from John Stevens Henslow offering Darwin a place on board the Beagle. DAR 97, f. B5v-B4r

Darwin wrote: ‘I owe more than I can express to this excellent man…I was strongly attached to natural history, and this attachment I owed, in large part, to him’. John Stevens Henslow was appointed Professor of Mineralogy at Cambridge in 1822 at the age of 26, and three years later was also awarded the Chair of Botany. He successfully campaigned for a new and much larger site for the Cambridge University Botanic Garden. Students, including Darwin, found Henslow’s lucid teaching – a mix of lectures, practical sessions and outings – very engaging. Darwin enjoyed Henslow’s botany lectures so much that he attended the course three times. He also accompanied Henslow on collecting expeditions, donating his finds to Henslow’s herbarium: these specimens of Matthiola sinuata, collected in Barmouth in August 1831 when Darwin was on a field trip with Sedgwick, are the earliest known to survive. By arranging several plants on one sheet, in a process he called ‘collation’, Henslow was able to analyse the limits of variation and so decide what constituted a species.