Philosophie Zoologique

Philosophie Zoologique ou exposition des considérations relatives à l'histoire naturelle des animaux

Title page of first edition, 1809
Author	Jean-Baptiste Lamarck
Country	France
Subject	Zoology, evolution
Publisher	Museum d'Histoire Naturelle (Jardin des Plantes)
Publication date	1809

Philosophie Zoologique ("Zoological Philosophy: Exposition with Regard to the Natural History of Animals") is an 1809 book by the French naturalist Jean-Baptiste Lamarck, in which he outlines his pre-Darwinian theory of evolution now known as Lamarckism.

In the book, Lamarck named two supposed laws that would enable animal species to acquire characteristics under the influence of the environment. The first law stated that use or disuse would cause body structures to grow or shrink over the generations. The second law asserted that such changes would be inherited. Those conditions together imply that species continuously change by adaptation to their environments, forming a branching series of evolutionary paths.

Lamarck was largely ignored by the major French zoologist Cuvier, but he attracted much more interest abroad. The book was read carefully, but its thesis rejected, by nineteenth century scientists including the geologist Charles Lyell and the comparative anatomist Thomas Henry Huxley. Darwin acknowledged Lamarck as an important zoologist, and his theory a forerunner of Darwin's evolution by natural selection.

Jean-Baptiste Lamarck (1744–1829) was a member of the French Academy of Sciences and a professor of botany at the Jardin des Plantes and then became the first professor of zoology at the new Muséum national d'Histoire naturelle. He became known for his work on the taxonomy of the invertebrates, especially of molluscs. However, he is mainly remembered for the theory that now bears his name, Lamarckism, and in particular his view that the environment (called by Lamarck the conditions of life) gave rise to permanent, inherited, evolutionary changes in animals. He described his theory in his 1802 Recherches sur l'organisation des corps vivants, and in his 1809 Philosophie Zoologique, and later in his Histoire naturelle des animaux sans vertèbres, (1815–1822).