Monday, June 22, 2009

Darwin's Barnacles

In 1836, Charles Darwin returned from his five year trip around the world on the Beagle. In 1837, he began writing out in notebooks the ideas that eventually would be elaborated as his theory of the origin of species. He married Emma in 1839. They moved to Down House in 1842, which would be their home for next 40 years until Darwin's death in 1882. By 1842, Darwin had written a thirty-five pages of a sketch of his theory of natural selection. By 1844, he had written a 231-page essay developing his theory. But then, oddly enough, he chose not to publish this work. Instead, in 1846, he began a meticulous study of barnacles that would not be completed until 1854. Only then would he return to his theory of the origin of species, and his Origin of Species was finally published late in 1859.

One of the big questions for Darwin scholars is why Darwin delayed the publication of his theory, and why he chose to spend eight years studying barnacles.

The best handling of this question is Rebecca Stott's book Darwin and the Barnacles (2003). This is one of the best books on Darwin that I have ever read. It is certainly one of the best-written. Stott is a novelist and a professor of English who writes with a wondrously evocative style.

Darwin's grandfather--Erasmus Darwin--had speculated in his book Zoonomia that all of life might have emerged ultimately from some simple aquatic life form. In 1844, Robert Chambers elaborated this idea in his Vestiges of the Natural History of Creation. Indeed, Darwin recognized in Chambers' book his own theory of transmutation of species as traced back to some original marine life form. But despite the wide audience for Chambers' book, scientists (including Darwin) criticized him for engaging in wild speculation without meticulous empirical research to back it up. This was a lesson for Darwin--that he should not publish his theory until he had won the respect of the scientific community for his careful observational and experimental research. His research on barnacles would do that.

In studying marine invertebrates to see the gradation of differences between life forms, Darwin was following in the tradition of Aristotle's biology, which was recognized by Robert Grant, who became Darwin's mentor in Edinburgh. But Grant and Darwin had advantages over Aristotle. The microscope allowed them to see microscopic patterns of life that were invisible to Aristotle. Another advantage for Darwin is that the development of a postal system and a railway system allowed Darwin to contact people around the world who might collect barnacle specimens and barnacle fossils for him, and with whom Darwin could carry on discussions about the problems he faced. Stott shows how this allowed Darwin to develop a "barnacle network" that would later expand as he carried out his later research from his perch in Down. This global network of information--based largely on the global structures of the British Empire--created the conditions for collective scientific research far beyond anything available to Aristotle.

Stott lays out at least five ways in which Darwin's barnacle research advanced his theory of the origin of species. First, this research allowed him to see how the history of barnacles showed the variability of animals adapting to diverse environments for survival and reproduction, and in this history, there was no sharp demarcation between one species and another. Second, this research established Darwin's authority as an empirical scientist who would not engage in broad speculation until he had mastered the details of natural history. Third, this work on barnacles gave him time to allow the pressure to build among naturalists who were beginning to recognize the mutability of species. Fourth, his global network of correspondence in his barnacle research established connections with people around the world that could later be used for promoting his theory of species.

Finally, this work on barnacles gave Darwin time to develop his writing style--in which he combines accuracy of description, cautious hesitancy, and boldness of conclusions. As she indicates, this deft combination of caution and boldness is illustrated by one sentence in the last paragraph of the Introduction to the Origin: "Although much remains obscure, and will long remain obscure, I can entertain no doubt, after the most deliberate study and dispassionate judgment of which I am capable, that the view which most naturalists entertain, and which I formerly entertained--namely, that each species has been independently created--is erroneous."

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