Introduction to Earthworms
Earthworms was Darwin’s last book.1 It was published on 10 October 1881, just six months before he died, and was reviewed enthusiastically in The Times that day praising Darwin for exalting ‘them of low degree’. The book was an instant success and remains a significant part of Darwin’s oeuvre. It is written in a clear, informal style and betrays, perhaps more than any of his other books, Darwin’s true delight in engaging with nature. Such was Darwin’s fame at the time the book appeared that the satirical journal Punch ran one of their ‘fancy portraits’ showing the wise old Darwin, sitting like a little girl in a garden, pondering a giant worm floating above him in the shape of a question mark. The caption states that Darwin ‘has lately been turning his attention to the “Politic Worm”’.
Darwin’s young protégé George Romanes, to whom he had entrusted some unpublished parts of his ‘big book’ on species, reviewed Earthworms in the weekly science journal Nature on 13 October. Romanes focused on Darwin’s astounding and totally original proofs of the intelligence of worms, while at the same time demonstrating that they were deaf and blind. Romanes cited, for example, Darwin’s experiments proving that worms selected which part of a leaf to pull down first into their burrows. Visitors to the Darwin Museum at Down House, his home from 1842 onwards, can today see the trappings of some of these experiments, such as the bassoon in the drawing room used to test worms’ response to deep notes. Another such worm-related item at Down House is a replica in the garden of the ‘worm stone’. This was used to measure the rate that stones sink slowly as worms digest the soil and deposit it above ground as worm casts, giant examples of which from around the world Darwin illustrated in his book.
In Earthworms itself Darwin returned, after decades devoted to mainly zoological, botanical and more overtly evolutionary works, to his first love: geology.2 Darwin considered himself a geologist during and for a decade after the voyage of the Beagle. Even though Darwin’s Journal of researches of 1839 covered a huge range of topics, his other sole author publications until the 1850s were almost all on geological subjects. Earthworms signaled this return to Darwin’s fascination for the way millions of small creatures, given time, can change the face of the Earth. The book was in fact a direct descendant of a paper on vegetable mould which Darwin read to the Geological Society in November 1837, just over a year after returning from his voyage round the world in the Beagle (Darwin 1838).
There are in fact strong thematic parallels between Earthworms and Darwin’s very first scientific monograph: Coral Reefs of 1842, which was the first of his ‘Geology of the Beagle’ trilogy. Indeed the last paragraph of Earthworms ends in typically lyrical Darwinian fashion, with an explicit comparison of the enormous geological power of earthworms and coral polyps:
When we behold a wide, turf-covered expanse, we should remember that its smoothness, on which so much of its beauty depends, is mainly due to all the inequalities having been slowly levelled by worms. It is a marvellous reflection that the whole of the superficial mould over any such expanse has passed, and will again pass, every few years through the bodies of worms. The plough is one of the most ancient and most valuable of mans inventions; but long before he existed the land was in fact regularly ploughed, and still continues to be thus ploughed by earth-worms. It may be doubted whether there are many other animals which have played so important a part in the history of the world, as have these lowly organised creatures. Some other animals, however, still more lowly organised, namely corals, have done far more conspicuous work in having constructed innumerable reefs and islands in the great oceans; but these are almost confined to the tropical zones. (p. 313)
At another point in the book (p. 256) Darwin also compared the soil which has passed through the gizzards of earthworms to the mud in coral atolls which has passed though worms and other creatures. This comparison is only one of many remarkable insights running through the book which make it highly relevant even today to geomorphologists, geoarchaeologists, ecologists, ichnologists, animal behaviourists, soil scientists, and other experts from '-ologies' not dreamt of in Darwin's lifetime. This introduction to Earthworms is intended not to duplicate Freeman’s bibliographical account, but rather to encourage more of these specialists and indeed anyone with a garden or allotment to read what is perhaps the most charming of all Darwin's books.
During the voyage of the Beagle Darwin became committed to a Lyellian view of nature as one in constant though mainly slow and gradual change. His thinking came to be dominated by a belief in vertical crustal mobility, in other words that the Earth’s surface was constantly oscillating in response to forces of uplift counterbalanced by subsidence elsewhere. The land in one part of the world, the Andes say, was rising from beneath the waves even as the coral-encircled extinct volcanoes of the South Pacific were sinking below them. By the end of the five-year voyage Darwin was convinced that the sea was the dominant force of erosion and he viewed landscapes such as the Blue Mountains of Australia or the lochs of Scotland as scenery sculpted by the sea before those countries had risen above it. We now know, and Darwin came painfully to realise with the advent of glacial theory in the 1840s, that ice and rain water could be just as, if not more powerful, given enough time.
Darwin’s first major scientific theory, expounded in brilliant style in Coral Reefs, was initially read in abstract to the Geological Society in May 1837. (Darwin 1837) In November of the same year he read his paper ‘On the formation of Mould’. This paper was based on some observations of the soil at Maer Hall, home of his uncle and soon to be father-in-law Josiah Wedgwood (or Uncle Jos), the man who had convinced Darwin’s father that son Charles should go on the Beagle voyage. Darwin had gone to Maer in September for some rest from his monumental post-voyage labours, but he could not resist while there doing some geology. Uncle Jos had noticed that lime and cinders spread on his fields had within a few years become buried. Jos’s explanation for this was that the lime and cinders were being buried by the soil from below them gradually being moved upwards and cast out from the intestines of worms.
It is interesting to note that in the original version of the ‘mould’ paper Darwin included a paragraph in which he made clear the comparison with the formation of mud on coral reefs and referred to this process as ‘a geological power’ which could explain how much of the famous Chalk Formation of Europe had been formed. In the final version of the paper published in 1840 in the Society’s Transactions, (Darwin 1840) this paragraph was omitted in response to William Buckland’s otherwise complimentary referee’s report (see Thackray 1984). There is a fascinating irony here in that Down House is built on the Chalk Downs of Kent (in fact the house and the surrounding village were both called ‘Down’ but the village was renamed ‘Downe’ to save postal confusion with Co. Down in Ireland). The Chalk underlies all of south east Britain and the surrounding seabeds and crops out across a vast area of the southern counties of England. Darwin and his various sons carried out a remarkable number of observations of the soil on the Chalk, many of which – such as those at Stonehenge and other ‘Druidical remains’ on Salisbury Plain - are described in detail in Earthworms.
In the Origin of species Darwin made the first attempt to quantify the number of years since the Chalk was deposited under the sea and he did this by estimating how long it would have taken the sea to erode the Kent and Sussex Downs as they were gradually upfolded while the Alps were rising in southern Europe. Darwin’s estimate, we now know from radiometric dating, was about three times too big, but it remained a brave attempt nonetheless. Darwin was anxious to show that the world was at least hundreds of millions of years old in order to give time for evolution to have occurred and it was a terrible blow to him when the physicist William Thomson (later Lord Kelvin) in the 1860s ‘proved’ that Darwin had massively over-estimated the age of the Earth (Herbert 2005). Kelvin at the time knew no more about radioactive decay than did Darwin so ‘ignored’ the possibility that the Earth had started cold and warmed up. Kelvin instead assumed that it had started as a ball of fire which had been cooling ever since. Darwin’s estimate of the age of the Earth is much closer to current estimates than Kelvin’s.
In Earthworms (p. 232) Darwin returned to the subject of the denudation of the Chalk and declared how his former belief that the sea was the most powerful agent of erosion had been superseded by a realisation of the power of air, frost and running rainwater:
Until the last twenty or thirty years, most geologists [i.e. the author of the Origin of species] thought that the waves of the sea were the chief agents in the work of denudation; but we may now feel sure that air and rain, aided by streams and rivers, are much more powerful agents,—that is if we consider the whole area of the land. The long lines of escarpment which stretch across several parts of England were formerly considered to be undoubtedly ancient coast- lines; but we now know that they stand up above the general surface merely from resisting air, rain and frost better than the adjoining formations. It has rarely been the good fortune of a geologist to bring conviction to the minds of his fellow-workers on a disputed point by a single memoir; but Mr. Whitaker, of the Geological Survey of England, was so fortunate when, in 1867, he published his paper "On sub-aerial Denudation, and on Cliffs and Escarpments of the Chalk."
Once Darwin moved to Down in 1842 he spread some Chalk over a pasture field to see how deep it would be buried ‘at some future period’ (Keith 1942). His energies for the next thirty years then became directed onto raising his family, publishing his Beagle geology, becoming the world’s authority on barnacles, publishing his great theory of evolution, firstly as a general theory then as a special theory for the origins of mankind, and finally onto the commencement of a series of fundamental contributions to plant science. Only in 1876, as a tired man in poor health, did he pick up the subject of worms again before, as he expected soon to be buried in Downe Churchyard3 joining the worms himself (Browne 2002, p. 479). It is quite staggering that in his remaining five years of productive life Darwin wrote his unpublished Autobiography, published a book about his famous grandfather Erasmus Darwin, plus two major botanical books and at least twenty journal contributions. All this in addition to virtually inventing the study of an aspect of soil science of incalculable importance to horticulture, agriculture and the global economy.
Darwin, C. R. 1882. The formation of vegetable mould, through the action of worms, with observations on their habits. London: John Murray. 7th thousand. Corrected by Francis Darwin. Text Image PDF F1364
1 The word ‘earthworms’ is used on the spine of the book, whereas the word used on the title page is ‘worms’.
2 Curiously, Herbert 2005 does not discuss Earthworms in her excellent study of Darwin’s geology.
3 Darwin was buried in Westminster Abbey.