Monday, June 15, 2009

The Philosophy of Sea Sponges: Aristotle, Grant, and Darwin

While travelling through Scotland last week, my family stopped to explore some beautiful coastal areas with tidal pools. Examining the life in those Scottish tidal pools reminded me of Robert Grant's study of the sea sponges that he found along the Firth of Forth near Edinburgh, and of how important Grant's work was in shaping Darwin's earliest zoological interests.

Some of the earliest proponents of evolution speculated that all life might have descended ultimately from some simple marine invertebrate. In the early 1820s, Grant studied sea sponges to show that they might be a descendant of those first living forms. After all, they seem to live at the border between plants and animals. Grant's experiments and careful observations led him to show that although sea sponges look like plants, they exhibit some of the activities of animal life such as digestion and voluntary movement.

In his research, he studied everything that had been written about sea sponges. He was especially intrigued by Aristotle's extensive work on sea sponges, showing that these creatures really were at the border of plants and animals. Grant saw himself as continuing the research that had been started by Aristotle. He studied Aristotle's text in the original Greek. He wrote:

"But the philosophy of the sponge, the immutable foundations on which scientific discriminations of the species ought to rest, the minute investigation of the mechanism, the composition, and the uses of all the parts of the animal, and of the extraordinary phenomenon it exhibits in the living state, --its mode of growth, --its kind of food, --its habits and diseases, --the means of cultivating an animal, which has so long rendered important services to mankind, --its mode of propagating the species, and extending them over the globe, and the great purposes which it is destined to fulfil in the universe, have remained where Aristotle left them, or rather, in this branch of study, mankind have gone backward ever since his time."

In 1826, Darwin came under Grant's influence when Darwin (at age 16) began work as a medical student at the University of Edinburgh. He found his medical training classes boring. But he enjoyed doing zoological studies with a group of Edinburgh students who had formed the Plinian Natural History Society, and Grant was the predominant influence over them.

Darwin presented a paper to this group--his first scientific paper--supporting Grant's view that the eggs of all zoophytes show spontaneous motion. Darwin continued this research on invertebrates during his voyage on the Beagle. Then he 1837, he made a note in his transmutation notebook about the importance of this for his emerging evolutionary thinking: "Prove animals like plants; trace gradation between associated & non-associated animals-- & the story will be complete."

Between 1846 and 1854, Darwin devoted all of his research to a massive study of all the species of barnacles, which established his scientific reputation before publishing his ORIGIN OF SPECIES.

This whole story of how Darwin's evolutionary reasoning was advanced by the study of marine invertebrates as first spurred by his time with Robert Grant is elaborated in Rebecca Stott's book DARWIN AND THE BARNACLE.

But for me the most interesting point here is how this illustrates the connection between Darwin's natural philosophy and the intellectual tradition of zoological research begun by Aristotle and then renewed by people like Grant.

That one could draw broad philosophical ideas from the study of seemingly insignificant organisms was a fundamental assumption of Aristotle's biology. But after Aristotle, few philosophers followed his lead. Modern natural philosophy renewed that Aristotelian tradition in the work that eventually led to Darwin's evolutionary science.

The thought that biological research might illuminate the deepest questions of philosophy--questions about the origins of life and natural order and the place of human life within that natural order--originated with Aristotle. The idea of bringing together modern biological research and philosophy as part of what I have called "Darwinian liberal education" has its roots in Aristotle's biological philosophizing.

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