Sunday, April 6, 2014

Everything Else Was Once Worms

I’ve been thinking about worms, a questionable action, for sure.  Why would anyone show an interest in worms?

Well, Charles Darwin (1809 – 1882) spent the last years of his life studying earthworms and writing The Formation of Vegetable Mould, Through the Action of Worms, With Observations on Their Habits (1881).  Apparently prompting the later suggestion by some that this signaled the man had entered his dotage; a trivial subject for failing faculties, I suppose.  I’m not in any way comparing myself to Darwin, though being accused of having failing faculties is a link.

In his 1982 essay on Darwin and worms, Stephen Jay Gould forcefully countered those critics, asserting, instead, that this last scientific writing was fully in keeping with Darwin’s complete body of work and that it was actually a clever way to enunciate, once again, a fundamental principle that underlay his understanding of nature:  given enough time, small processes lead to large changes.  With worms,
Darwin had chosen well to illustrate his generality.  What better than worms:  the most ordinary, commonplace, and humble objects of our daily observation and dismissal.  If they, working constantly beneath our notice, can form much of our soil and shape our landscape, then what event of magnitude cannot arise from the summation of small effects.  (Gould, Worm for a Century, and All Seasons, as excerpted in The Oxford Book of Modern Science Writing, edited by Richard Dawkins, 2008, p. 205.)
I don’t think it undercuts Gould’s argument to suggest that Darwin might have also appreciated earthworms as a subject of sustained study because of his long standing interest in the invertebrate, and, perhaps most importantly, because much of the analysis could be done without leaving the sanctuary of Down House.  Physically, the man was showing his age.  As Janet Browne wrote in her magnificent two volume biography of Darwin,
It was a perfect project for a man with his circle of landed connections.  Perfect, too, for a slow-moving country gentleman with a penchant for leisurely, appreciative walks at home and on the estates of friends and relatives.  (Charles Darwin:  The Power of Place, volume two of the biography, p. 447.)
Incidentally, when it came out in 1881, Darwin’s book on worms became a best seller.

Perhaps it is appropriate now that Spring seems to have actually arrived that my thoughts have gone to worms.  Turn over the soil in flowerbeds that have lain dormant for the winter, and discover pulsating, stretching, contracting earthworms, harbingers of good things to come.  Yes, an appropriate rationale, but, no, early gardening isn’t why I’ve been thinking about worms.  The objects pictured below are the reason.

A few days ago, in a quiet moment and in a little tray of material from the Oxford Clay Formation in England, I discovered these small fossils and they have everything to do with worms.  Worms’ soft bodies generally don’t fossilize, though fossilized traces of worms seem common enough, such as tracks left by moving worms and burrows filled with stone.  What’s shown above are pieces of the calcareous tubes secreted by marine worms in the Upper Jurassic (Oxfordian stage, 161 to 156 million years ago).  The worms living in these tubes were, I think, Genicularia vertebralis (J. de C. Sowerby), a free living worm that was not physically attached to the interior surface of the tube in which it lived.  The interiors of these tube fragments are now filled with matrix.

I base my identification on Fossils of the Oxford Clay, edited by David M. Martill and John D. Hudson (1991, p. 174 – 176), and British Fossils:  Mesozoic, edited by Andrew B. Smith (Natural History Museum, 2012, plate 4, figure 3).  I will ignore the nagging little voice that says this might be an instance of naming the record or trace of an animal’s action, not the animal itself, which would make this an ichnofossil.

Genicularia vertebralis were annelids or segmented worms, members of the Annelida phylum, as are earthworms.  Annelids have complex organs, including blood vessels, a nervous system, and a digestive tract; their bodies are formed of ringed segments.  Of note, when it comes to complexity, Darwin spent time trying to build a case that earthworms had some form of intelligence.

Taxonomically, worms have had a difficult history.  In 1758, the father of scientific taxonomy, Carl Linnaeus (1707 – 1778) divided all animals into just six, decidedly unequal, groups, unequal in the number of members in each and unequal in the affinities that might have logically bound members to that group.  Animals, he posited, consisted of mammals, birds, reptiles, fishes, insects, and everything else.  Well, he didn’t actually use that name for the last category, instead he labeled it vermes (worms).

In 1809, naturalist Jean–Baptiste Lamarck (1744 – 1829), professor at the Muséum d’Histoire Naturelle, and often considered one of Darwin’s foils for his thoughts on evolution, rebelled against the vermes group, describing it, in Philosophie Zoologique, as “a kind of chaos where very disparate objects have been united together,” and as a “monstrous class.”  In his essay A Tree Grows in Paris:  Lamarck’s Division of Worms and Revision of Nature, Stephen Jay Gould labeled the group a “wastebucket.”  This particular label, he noted, was a
semitechnical term among professional taxonomists, a description for inflated groups that become receptacles for heterogeneous bits and pieces that most folks would rather ignore . . . .  (The Lying Stones of Marrakech, 2000, p. 130.)
(The quotations from Lamarck’s Philosophie Zoologique were translated by Gould.)

It must have been particularly galling to Lamarck that, officially, he was the professor of insects and worms.

Over time, the worm wastebucket has been significantly reduced, and many significant phyla have emerged, among them Crustacea and Arachnida – Lamarck’s work.  He was also responsible for creating the Annelida.  Today, worms are found in several phyla, besides Annelida, including Nematoda (nematodes or roundworms) and Nemertea (ribbonworms).

Though I’ll continue, on rainy days, to pick through my Jurassic period material, looking for worm fossils, it’s time to take the trowel, venture outside, and turn over some garden soil, pleased, as always, to encounter those annelids that so intrigued Darwin.  When naturalist and longtime friend Joseph Dalton Hooker (1817 – 1911) wrote to Darwin, thanking him for a copy of the recently published earthworm book, he commented with gentle humor,
I take shame to myself for not having earlier thanked you for the Diet of Worms, which I have read through with great interest.  I must own I had always looked on worms as amongst the most helpless and unintelligent members of the creation; and am amazed to find that they have a domestic life and public duties!  I shall now respect them, even in our Garden pots; and regard them as something better than food for fishes.  (Life and Letters of Sir Joseph Dalton Hooker, Volume 2, edited by Leonard Huxley, p. 255.)

No comments:

Post a Comment

Nature Blog Network