GEOFFROY SAINT-HILAIRE, ETIENNE. - Zoologist and palaeontologist, born at Etampes (Seine-et-Oise) on 15 April 1772, died in Paris on 19 June 1844. Professor of zoology at the Sorbonne. A friend of Lamark and follower of his transformed theories, he recognized a factor of modification in the gradual depletion of oxygen in the air. He further maintained that variations in species are abrupt (in this fact may be seen the germ of mutationist theory) and due to anomalies of the embryo caused by rapid changes in the environment (as occurs in monstrosities). At first a friend and then an adversary of Cuvier, he engaged with him in polemical debates at the Academy.
He was the author of the Loi du balancement des organes, according to which the development or diminution of one organ occurs respectively to the detriment or advantage of another organ.
During the French Revolution and in July 1830 he worked with self-sacrifice and courage to help priests escape and to conceal them, among them the celebrated Hally; a Catholic, though not a practising one, he had a lively trust in Providence, especially during his blindness and old age.