John Stevens Henslow (1796–1861)

John Stevens Henslow was a brilliant botanist and geologist, an ordained a priest in the Church of England and a generous philanthropist. He spent much of his working life in the University of Cambridge, and made his name in the wider world as mentor to Charles Darwin. This article explores the remarkable life of this talented nineteenth century cleric who made a lasting contribution within Cambridge University and the wider education system of his day.

Revd Professor John Stevens Henslow
The Revd Professor John Stevens Henslow 

Early life

Henslow was born on 6th February 1796 in Rochester, Kent. He was the eldest of eleven children. His father, a solicitor, encouraged him to develop his enthusiasm for natural history and, at a very early age, he became an avid collector of botanical specimens.

In 1814, Henslow entered St John’s College, Cambridge, where he studied science. He graduated in 1818, and then renewed his interest in natural history, making geological expeditions to the Isle of Wight and the Isle of Man with his Cambridge colleague Adam Sedgwick, one of the founders of modern geology.  In 1821 the two men established the Cambridge Philosophical Society as a debating forum and means of disseminating knowledge in mathematics and the natural sciences. The following year, the University offered Henslow the chair of mineralogy which he took up with great enthusiasm.


Two years later he was ordained and, in 1825, became the curate at Little St Mary’s Church, Cambridge. In the same year, he was offered the position as Regius Professor of Botany – a post he held for the rest of his life.

Henslow was a popular, progressive teacher, both in the classroom and in the field. His natural enthusiasm made botany one of the more popular subjects at the university. Rather than pampering his students, he encouraged them to make their own observations.  He gave them plants, asking them to examine and record their individual structural characteristics. He took them on field trips, and invited them to his house for dinner.  There they discussed a range of scientific topics more informally.

The Botanic Garden, Cambridge
The Botanic Garden, Cambridge

However, Henslow had few botanical resources for his enlightened approach. The old University herbarium was rapidly decaying, and the small Botanic Garden was inadequate.

Instead, he envisaged a new and bigger Botanic Garden able to serve two different communities. It was to become a place of scientific study for the University.  But he also wanted a place of recreation and learning for the whole community. So he set about extending the site.

In 1830, he identified a 40-acre area of cornfields just south of the city boundary. The University commissioned a botanic garden plan for the entire area.

Henslow supervised the the planting of new trees, shrubs and plants, many of which came from overseas.  His two founding strands – University and community – remain enshrined in the research and public engagement that continues in the Botanic Garden. He was its crucial founder, making it world-famous to this very day. Nevertheless, this academic clergyman was to play an even more crucial role in his academic field.

Mentor to Charles Darwin

Today historians best remember Henslow as friend and mentor to his pupil Charles Darwin, and for inspiring him with a passion for natural history.

The two met in 1828. The young Darwin, who had enrolled to study theology at Christ’s College, began attending Henslow’s Friday-evening scientific soirées.

Henslow became his tutor. Soon, he marked out Darwin as a promising student. Indeed, his star pupil became a lifelong friend – a remarkable alliance which persisted, in spite of Darwin’s eventual atheism and Henslow’s never-failing liberal Christian faith.

After Darwin’s graduation, Henslow persuaded him to study geology, and arranged for him to become a field assistant to Adam Sedgwick and help on some research in north Wales. Little did any of them realise just how soon Darwin would be putting his newly acquired skills to the test.

Henslow’s colleague The Revd Professor Adam Sedgwick
Henslow’s colleague the Revd Professor Adam Sedgwick

Henslow was offered a post as naturalist to sail aboard the survey ship HMS Beagle on a planned two-year trip to survey South America.  However, his wife dissuaded him from accepting. Seeing a perfect opportunity for his protégé, the good-natured clergyman wrote to the ship’s captain, Robert Fitzroy, telling him that Darwin was an “acute observer” and the ideal man to join the expedition team.

Darwin sets sail

A few months later, Darwin set sail for the South Seas.  This turned out to be a round-the-world voyage of nearly five years – including a visit to the Galapagos Islands, where he discovered unique flora and fauna.

During the Beagle voyage, Darwin and Henslow wrote to each other as often as the primitive postal system would allow. Henslow encouraged Darwin, and advised which specimens to collect, recommending the best way of preserving and shipping them.

As the main recipient of Darwin’s massive collection of scientific samples, Henslow passed them on to the appropriate experts to analyse. He published extracts of Darwin’s letters in scientific journals and presented summaries to the Cambridge Philosophical Society.

When, in 1836, Darwin returned home, Henslow helped him obtain funding to publish his zoology books. His scientific credentials and future scientific career were assured – thanks largely to Henslow.

From university to parish priest

The following year, Henslow became Rector of the parish of Hitcham in Suffolk. This marked a turning-point in his life. and he remained there for the rest of his days.

Hitcham was a remunerative Crown living for its Rector. But its parishioners were poor and most people would have been illiterate.  The great university academic was an uninspiring preacher. His congregation was barely big enough to fill a single pew. Instead, he decided to concentrate on improving his parishioners’ well-being through scientific, rather than spiritual, enlightenment.

Queen Victoria with her five children
Queen Victoria with her five children

Education had to be paid for. So Henslow both raised funds and donated his own money to set up a school in 1841. He taught some of the lessons himself. Among his many books, he published a standard work on the flora of Suffolk. He identified the plants which the schoolchildren found in his parish. By 1860 he had recorded 406 species. A hundred years later, 60 of these could no longer be found.

Henslow engaged in many other philanthropic endeavours. During the so-called hungry 1840s, severe economic depression and serious crop failures across Europe led to widespread famine. He reacted to the crisis by letting 52 allotments on land owned by the parish church.

However, local employers were infuriated at this use of glebe land.  They decided to refrain from hiring any labourers who rented an allotment. Even so, the scheme caught on and, two decades later, 150 allotments were under cultivation in the village.

He founded the Ipswich Museum in 1847, becoming its president in 1850. He administered local charities, and organised educational excursions to various venues, including the 1851 Great Exhibition.

His contribution to agriculture

By and large, Henslow devoted his energy on improving the lot of his parishioners, but his scientific influence spread far and wide. He showed Irish farmers, stricken by the potato famine (1845–46), how to extract starch from rotten potatoes, and gave public lectures on the fermentation of manure.

In spite of his parish duties, he continued to carry out archaeological excavations.  He made numerous discoveries in East Suffolk. While on holiday in Felixstowe, he discovered phosphate-rich coprolite nodules – fossilised faeces or bones – in the Red Crag cliffs.

At this time, scientists were researching and experimenting with different chemicals in an attempt to find suitable fertilisers.  In particular their interest focused on the chemical content of naturally-occurring rocks and minerals.

Henslow knew that the Cambridgeshire greensand and river valleys in east Suffolk were abundant sources for phosphates. So he advocated the use of phosphates to improve crop yield in agricultural crops in the region. He also disseminated the findings arising from field experiments that tried out various fertilisers and measured the resulting product.

Although he derived no financial benefit, Henslow’s discoveries played an important part in the establishment of the fertiliser industry. Famous names include Joseph Fison, who set up works in Ipswich and a depot in Hauxton near Cambridge. Among other beneficiaries from his research were the Prentice brothers in Stowmarket.  They exported superphosphates around the world from the port at Ipswich.

Henslow’s last year

Henslow’s widely acclaimed achievements kept him in contact with many distinguished and prominent people. He tutored Queen Victoria’s children, and kept in touch with the wider scientific community, including his celebrated former pupil, Charles Darwin.

The year before his death, Henslow chaired the legendary 1860 Oxford evolution debate on Darwin’s theory of natural selection.   Thomas Huxley and Henslow’s son-in-law, Joseph Hooker, were among  those defending Darwin against Bishop Samuel Wilberforce.

The following winter, Henslow became seriously ill with a heart condition. His health continued to grow worse. Realising that the end was near, with Hooker standing vigil, he bade farewell to numerous visitors called to his bedside. Conspicuous by his absence was Charles Darwin, by now a virtual invalid himself.

John Stevens Henslow died after a bronchial attack on 18th May 1861. He is buried in Hitcham churchyard. Charles Darwin wrote to Hooker, saying, “I fully believe a better man never walked this earth.”

© Owen Spencer-Thomas

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