Jean-Baptiste Pierre Antoine de Monet, chevalier de Lamarck (1 August 1744 – 18 December 1829) was a French naturalist. He was a soldier, biologist, and academic, and an early proponent of the idea that biological evolution occurred and proceeded in accordance with natural laws.

In 1801, he published Système des animaux sans vertèbres, a major work on the classification of invertebrates, a term he coined. In an 1802 publication, he became one of the first to use the term "biology" in its modern sense. Lamarck continued his work as a premier authority on invertebrate zoology. He is remembered, at least in malacology, as a taxonomist of considerable stature.

The modern era generally remembers Lamarck for a theory of inheritance of acquired characteristics, called soft inheritance, Lamarckism, or use/disuse theory, which he described in his 1809 Philosophie Zoologique. However, the idea of soft inheritance long antedates him, formed only a small element of his theory of evolution, and was in his time accepted by many natural historians. Lamarck's contribution to evolutionary theory consisted of the first truly cohesive theory of biological evolution, in which an alchemical complexifying force drove organisms up a ladder of complexity, and a second environmental force adapted them to local environments through use and disuse of characteristics, differentiating them from other organisms.

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