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

In the book, Lamarck names two supposed laws that would enable animal species to acquire characteristics under the influence of the environment.

The first law states that use or disuse will cause body structures to grow or shrink over the generations.

The second law asserts that such changes will be inherited.

Those conditions together imply that species continuously change by adaptation to their environments, forming a branching series of evolutionary paths.

Lamarck is largely ignored by the major French zoologist Cuvier, but he attracts much more interest abroad.

The book is read carefully, but its thesis rejected, by nineteenth century scientists including the geologist Charles Lyell and the comparative anatomist Thomas Henry Huxley.

Charles Darwin will acknowledge Lamarck as an important zoologist, and his theory a forerunner of Darwin's evolution by natural selection.