Worms may not be the most exciting of creatures to describe or discuss. They are disgusting, slimy things we see after a heavy rainfall or when we begin spade work in the garden. There is nothing extremely important, one may suspect, about these creatures. So why did Charles Darwin write an entire book on them in an advanced stage of life?
Not too long ago I thought these things upon reading a somewhat intriguing article on some fossilized forms. My thoughts quickly diverted to my copy of The Formation of Vegetable Mould through the Action of Worms, a handsome 1907 edition. The original was first published in 1881, a year before Darwin’s death. Darwin was known for looking at the big picture, but also at times returning to excruciating detail of things small. He understood the biology of so simple a creature to have such a great influence over the geography of his land: “… the whole country has passed many times through, and will again pass many times through, the intestinal canal of worms”. He would profess “worms have played a more important part in the history of the world than most persons would at first suppose.” The creation of fertile ground by the actions of an unassuming and innocuous creature could only be glorified by so fine a naturalist.
Stephen Jay Gould marveled at Darwin’s choice of research matter in one of his essays from the magazine Natural History, and reproduced in Hen’s Teeth, Horses Toes (1984). The essay, ‘Worm for a Century’ was an inventive one, plucking a long forgotten piece, and shining it up for all to appreciate. “I would rather peruse 300 pages of Darwin book on worms” he wrote “than slog through 30 pages of eternal verities explicitly preached by many writers” (p. 129). Gould, who was aware of the linear chain of book production by Darwin, mocked the usual practice: “Most eminent greybeards [who know their time is coming] sum up their life’s thoughts and offer a few pompous suggestions for reconstituting the future” (p. 120): But not Darwin. He found the most un-titillating piece of natural history, and found purpose and relevancy in constructing a pattern of top soil production, and the inter-relations between life and its surroundings.
It is ironic though, that Gould, the flag bearer for all that is Darwin in the 20th century, would not follow in his footsteps. Gould’s last book, The Structure of Evolutionary Theory, written when he knew his time was approaching, fell into the category of the ‘greybeards’ than a Darwiniate student.
Palaeontological evidence of worms is difficult to find. Therefore, their role in the changing landscape of days gone by can, for the most part, only be inferred. Much of the evidence comes not from fossilized remains of worms, but by their burrows left behind. And as a most bizarre occurrence, burrows of worms found right after the Cretaceous extinction event was certainly a highlight of new discoveries. Last year in the on-line peer-reviewed journal PLoS ONE, a team led by Karen Chin announced the discovery of fossil worm burrows in the geological moments after the extinction event 65 million years ago. Dr. Chin, we may recall, was the lead author on the article in Nature many years ago announcing the discovery of the first coprolite from a likely Tyrannosaurus from the Frenchman Formation of Saskatchewan.
The trace fossils come from North Dakota, in a series of “crisscrossing networks of horizontal burrows”. The placement in the rock layer indicates that they were deposited less than 10,000 years after the geochemical signatures that mark the event. It can easily be assumed that recovery after the extinction event for some groups like these earthworms was rapid. The worms themselves would provide sustenance for carnivores: “the survival of carnivorous mammals, birds and other vertebrates in the early Cenozoic would have depended on the availability of prey …” and may even hold their key to survival after such a near apocalyptic event.
Of course it would be impossible to rightly suggest or postulate what Darwin’s response would be to such a discovery. But knowing his meticulous nature and a subject he held so dearly, we could stretch it just a bit couldn’t we? In the concluding remarks in his ‘worm book’ is just one of the tell-tale relevance’s Darwin ascribed to this lowly a creature:
“The plough is one of the most ancient and most valuable of man’s inventions; but long before he existed the land was in fact regularly ploughed, and still continues to be thus ploughed by earth-worms.”