John Stevens Henslow

Professor John Henslow was a British botanist, clergyman, and geologist who popularised botany at the University of Cambridge by introducing new methods of teaching the subject. Notably he initiated the move of Cambridge University Botanic Garden to its present site in 1846 and was mentor to Charles Darwin, encouraging him to think about the importance of plant diversity.

Henslow was 29 years old when he accepted the Chair of Botany in 1825, becoming the fourth Professor of Botany at the University of Cambridge. Botany was at a very low ebb in the University at this time and no lectures had been given for 30 years. He was also given responsibility for the original Botanic Garden (founded in 1762), in the centre of the city where plants were cultivated for medical studies.

Henslow wanted to change this. He believed a much larger site was needed for the study of all kinds of plants for scientific research. His vision was to establish a site with a major tree collection and arrange trees and plants to show their family relationships, to illustrate ideas about how plants of the same species varied – a theory taken up by his most famous student, Charles Darwin.

In 1831 he convinced the University to move its Botanic Garden from the cramped city centre location to the current 40-acre site (though there was only funding supplied at that time for development of the western 20 acres). Plantings were arranged to reflect Henslow’s fascination with plant variation and diversity. Trees were grouped together in their families outside the Garden’s perimeter path and herbaceous plants grouped in families in the Garden’s Systematic Beds, laid out by the Garden’s first curator appointed by Henslow, Andrew Murray.

Henslow taught his students botany in the tradition of natural theology, which was the idea of studying the extent and utility of God’s creation. However, he was also considered quite revolutionary at the time in his way of looking at things in a systematic way. At a time when plants were seen as part of God’s unchanging creation, Henslow pioneered research into the idea of variation in plant species as he wanted to understand the variations, ranges and boundaries of plant species.

He took his students out into the field on collecting expeditions, teaching them how to observe plants and encouraging them to make observations of their own. They were asked to examine and record the characteristics of the structures they found. This method, combined with unusual field trips, interesting lectures, and Henslow’s natural enthusiasm, made botany one of the most popular subjects at the university. His class list would extend to as many as 80 students, at a time when the total University population was only in the low hundreds. One of the students Henslow served as a source of inspiration for was Charles Darwin, whom he taught between 1829 and 1831.

Henslow was also a good artist and produced a range of colourful botanical wall charts and diagrams, which he used for teaching his students. He also sent his students – many of them training to be priests – on trips around the world, encouraging them to send him back specimens which he pressed and mounted to demonstrate the wonders of God’s creation.

Between 1821 and 1835 Henslow expanded and reorganised the Cambridge University Herbarium, adding over 10,000 specimens from across Britain and the wider world. It became the basis for the Cambridge University Herbarium that we know today. He organised his herbarium to emphasise variation within species and determine the limits between species. To aid him, he enlisted about a hundred collaborators, one of whom was the young Charles Darwin.

This influence was far-reaching, with Charles Darwin following Henslow’s teachings for many years. In fact, it was Henslow who was first invited to embark on the Voyage of the Beagle but due to his responsibilities to his family, teaching and parish, he nominated Darwin to go and observe, collect and note the natural world. The Voyage proved groundbreaking – with Darwin using it to demonstrate that with the variation of species over time, new or different species can evolve. The thinking and theorising with Henslow laid out a path for Darwin’s subsequent evolutionary theories.

Darwin took his famous trip on the HMS Beagle in 1831. Visiting the Galapagos islands, Darwin began by arranging his observations in a framework set out by Henslow which assumed the stability of species. In recent years, academics have put forth that the instruction Darwin received from Henslow set the framework for the new understanding Darwin came to: that varieties are incipient species. Darwin’s theory of mutability would later find its full expression in his canonical On the Origin of Species first published in 1859.

In 1837, Henslow secured the rectorship of Hitcham, Suffolk, where he stayed for the rest of his life.

He had a significant and progressive impact on his parish with many innovations including switching traditional church handouts to the poor from money, to coal and clothing. Allotments were provided so people could grow their own food and with the expansion of the railways he organised excursions to London, Cambridge and Norwich, so his parishioners could expand their horizons. He won over his congregation, many who were farmers, by encouraging them to experiment with fertilisers to help with their yields – his findings prompted two Suffolk farmers to set up Fisons, now an international chemical company.

Henslow also raised funds and donated his own money to set up a village school and led many of the lessons himself, with many of the children acquiring considerable botanical knowledge.

Alongside this, Henslow found the time to travel regularly to London, where he tutored Queen Victoria’s children.

Henslow died at Hitcham from an attack of bronchitis aged 65 in 1861. During his life, he remained a mentor and friend to Charles Darwin. Other famous students and contemporaries of Henslow included Miles Joseph Berkeley, Cardale Babington, Leonard Jenyns, Richard Thomas Lowe and William Hallowes Miller.

Read Unveiling Darwin’s treasures – which includes a special section about the little-known relationship between Charles Darwin and his innovative teacher, of whom he wrote “a better man never walked this earth”.