(1744–1829), French naturalist, whose great breadth of understanding of plants and animals led him to insights about evolution, 50 years before Charles Darwin’s Origin of the Species. Because his theory of the inheritance of acquired characteristics became the center of stormy debates and because this theory was later disproved by the Austrian botanist Gregor Mendel’s studies in HEREDITY, (q.v.), Lamarck’s contributions in systematic zoology have been largely neglected.

Born Aug. 1, 1744, in Bazentin, France, and educated for the priesthood, Lamarck joined the French army and then studied medicine in Paris, where he became interested in botany. In his first important work, Flore Française (French Flora, 3 vol., 1778), he developed a new system for the accurate identification of plants by means of an analytic key. The work led to his association with the French naturalist comte Georges Louis de Buffon, his election to the Academy of Sciences, and his appointment as curator of the herbarium at the Royal Botanical Garden (Jardin du Roi) in Paris. After travels through Europe as royal botanist, he began writing the Dictionnaire de botanique (Dictionary of Botany, 4 vol., 1783–96) and Illustrations de genres (Illustrations of Species, 1885). He became professor of botany at the Jardin in 1788 and professor of zoology in 1793, a position he retained until 1818.

As a zoologist Lamarck proposed the classes Annelida, Arachnida, Crustacea, Infusoria, and Tunicata, which, with modification, are still accepted as taxonomic units (see TAXONOMY,). He was also responsible for the division of the animal kingdom into invertebrate and vertebrate subkingdoms, a distinction that was adopted in the later 19th century.

Lamarck’s great overview of biology—a word he was the first to use—and his classification studies, especially of living and fossil mollusks, led him to speculate that species evolve from simpler organisms over huge spans of time. Following through with this then-revolutionary and unpopular idea, he boldly proposed in Philosophie zoologique (1809) that animals acquire different characteristics in response to their environment. Thus, in his often-cited example, a giraffe by stretching its neck to reach foliage, passes on the characteristic of an elongated neck to the next generation. A half century later, when Darwin proposed instead that evolutionary change takes place randomly by natural selection, Lamarck’s theory of acquired characteristics, which was given the name Lamarckism, became fervently opposed by the pro-Darwinists. When Mendel’s experiments showed that no change in the body can affect the genes, Lamarckism became discredited, although it had a revival in the Soviet Union during the Stalin era (see LYSENKO, Trofim Denisovich).

Lamarck’s solid contributions in biological classification are recognized today. He is considered an important forerunner of evolutionary theory and among the first thinkers to break away from long-held views of the origin of life. In his own day Lamarck’s work was largely neglected. For the last decade of his life he was blind and lived as a pauper; he died in Paris on Dec. 18, 1829.