GEOFFROY SAINT-HILAIRE, ETIENNE. Zoologist and paleontologist, born at Étampes (Seine-et-Oise) on 15 April 1772, died in Paris on 19 June 1844. Professor of zoology at the Sorbonne. Friend of Lamarck and follower of his transformist theories, he recognized a factor of modification in the gradual impoverishment of the oxygen in the air. He also maintained that variations in species occur suddenly (in this view one can see the germ of mutationist theory) and are due to anomalies in the embryo caused by rapid environmental changes (as happens in the case of monstrosities). He was first a friend and then an opponent of Cuvier, with whom he engaged in polemical discussions at the Academy.
Author of the *Loi du balancement des organes*, according to which the development or reduction of one organ respectively disadvantages or does not disadvantage another organ.
During the French Revolution and in July 1830, he worked with self-denial and courage to help priests escape and go into hiding, among them the celebrated Haüy; a Catholic, though not a practicing one, he had a lively faith in Providence, especially during the period of his blindness and old age.