The Eighteenth-Century French Scientist ÉTienne Geoffroy Saint-Hilaire Argued for a Far-Reaching

question 18

Essay

The eighteenth-century French scientist Étienne Geoffroy Saint-Hilaire argued for a far-reaching concept of what we would now call homology.For example,he argued that the vertebrae and ribs of vertebrates are fundamentally the same structures,built on the same plan,as the segmented exoskeleton and legs of insects and other arthropods.Insects,according to Geoffroy Saint-Hilaire,quite literally live inside their vertebrae and walk on their ribs.His idea is not really true in the sense that he conceived it―and yet,in the light of discoveries about Hox genes and developmental regulation,some modern evolutionary biologists have had good things to say about Geoffroy Saint-Hilaire's work.(See "Brotherhood by Inversion" in Stephen Jay Gould's book Leonardo's Mountain of Clams and the Diet of Worms,for example.)Explain why a modern "evo-devo" specialist might find Geoffroy Saint-Hilaire's ideas worth revisiting in the light of current knowledge.

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