Jean-Baptiste Lamarck is well known as a pre-Darwinian proponent of evolution; however, comparatively little has been published on his views of human physiology and development. This paper argues that the will was of particular importance in Lamarck’s social commentary, and contextualizes his ideas in light of prevailing debates in France about the physiology of mind and morals and the future development of the French nation. The paper first examines popular misconceptions of Lamarck’s ideas about the role of the will in evolution, particularly those perpetrated by Georges Cuvier and Charles Lyell; then it analyzes Lamarck’s genuine argument that human physiology could be altered by manipulation of a person’s habits and milieu. This belief led him to treat natural transformation and social change as complementary forces, and the will was the linchpin in this linkage. Finally, the paper suggests that Lamarck’s theories about the role of voluntary action in evolution should be understood in the context of French national concerns about degeneration, social reform, and human perfectibility, which remained part of the French intellectual landscape throughout Lamarck’s life and career.