A professor at twenty-one and member of the Napoleon's Egyptian expedition at twenty-six, Geoffroy Saint-Hilaire was a man of one idea, which he formulated when he was twenty-four. Nature, he thought, had formed all living beings with one single plan.

This was a revolutionary idea—and one vigorously opposed by Geoffroy's colleague Georges Cuvier, a great anatomist and one of the giants of French science. In 1830, their long-running disagreement erupted into furious public debate. Geoffroy argued that all vertebrates shared the same basic body plan not just with each other but with insects as well. Cuvier strenuously disputed this idea, which he saw as tantamount to a belief in "transformism"—arguing instead that each species had its own special and permanent form.

With Geoffroy Saint-Hilaire, Hervé Le Guyader provides an analysis not only of that infamous debate but also of Geoffroy's bold intuitions about anatomy and development. Featuring Geoffroy's published version of the 1830 debates—translated into English for the first time—the book also illustrates how Geoffroy's prescient insights foreshadowed some of the most recent discoveries in evolutionary and developmental biology.