The man who turned down the job of naturalist on HMS Beagle

On August 13th. 1831 Reverend  John Stevens Henslow, Professor of Botany at the University of Cambridge, received a letter asking him to recommend a suitable gentleman ship’s naturalist to accompany Robert Fitzroy, Captain of HMS Beagle, on a circumnavigation of the world.

Henslow, the finest field botanist of his day, would have been the prime candidate but family responsibilities stood in his way. His next thought was to nominate his brother-in-law, Reverend Leonard Jenyns but he declined in favour of tending to the spiritual needs of his parishioners.

So by the end of August Henslow had offered the job to Charles Darwin, his student protégé at Cambridge. The rest is (natural) history.

But what if Henslow, a creationist until the day he died in 1861, or his cleric brother-in-law Leonard Jenyns, had sailed with Fitzroy? It seems unlikely that they would have come up with a theory of evolution. If Charles Darwin’s date with destiny had never arrived it would have been left to some other scientist, in another place and at another time, to provide the theory that underpins all of modern biological science. 

But Jenyns, in his own way, made a lasting contribution to science too – a contribution that is very relevant to the turbulent climatic times that we live in.

It can be found in this little book, A Naturalist’s Calendar, published in 1907 and edited by Francis Darwin, Charles Darwin’s son.

Stay-at-home Jenyns, who by this time had changed his name to Leonard Blomefield in order to claim an inheritance, was curate of Swaffham Bulbeck in Cambridgeshire from 1823 to 1849 and during that period kept detailed phenological records of natural events in his parish. While Charles Darwin, whom remained a life-long friend, was pondering on Galapagos finches and giant tortoises, Jenyns was recording the annual date when local frogs spawned or primroses bloomed.

Phenology, the study of the timing of natural events, is an important science today because observing the changes in ways in which the life cycles of plants and animals respond to climate provides some of the best evidence that the climate really is changing. Jenyns’ meticulous records, for scores of familiar plants and animals, record the earliest and latest dates of phenological events and also the mean dates. They provide a reliable datum point for comparisons in today’s warmer world.

Nature's Calendar the citizen science phenology web site where we can all monitor the natural changes brought about by climate change, is a modern day manifestation of Jenyns' work.

When Jenyns made his observations it must have seemed like a simple pastime for a parson-naturalist with time on his hands – the kind of observational recording that is often today sneered at by experimental scientists. As it has turned out, the results of his curiosity and dedicated recording have become highly relevant to our modern predicament.

I’m typing this on a mid-December evening when the temperate outside is warmer than many a spring day, after one of the warmest Novembers on record. I wonder what Jenyns would have made of that.