Lamarck , Jean Baptiste Pierre Antoine de Monet, Chevalier de

(1744–1829) French biologist

Lamarck was born at Bazantin in France. Although his parents had intended him to enter the Church, when his father died in 1759 Lamarck left his Jesuit school and joined the army, where he was honored for his bravery in the Seven Years' War. He became interested in botany during his postings to camps in the Mediterranean and eastern France and completed his Flore française (Flowers of France) in 1778, having left the army some ten years earlier because of poor health.

To simplify the identification of plants, Lamarck presented the flora as a dichotomous key (a systematic list of characteristics in which there are two choices at each step in the classification). This system, which was far easier to use than other classifications of the time, impressed Georges de Buffon, who arranged for it to be published and also ensured that Lamarck was elected to the French Academy of Sciences.

Lamarck was employed as botanist at the Jardin du Roi until the institute was reorganized during the French Revolution. In the newly named Muséum National d'Histoire Naturelle Lamarck was placed in charge of animals without backbones – a group he later named ‘invertebrates’. He differentiated the arachnids, insects, crustaceans, and echinoderms and wrote a seven-volume Natural History of Invertebrates (1815–22).

Lamarck was also interested in meteorology, geology, chemistry, and paleontology and it is thought that his observations in these fields contributed to the formulation of his evolutionary theory, which he first put forward in Zoological Philosophy (1809). Until the late 1790s, he had believed that species remained unchanged, but fossil evidence, and his nonbelief in extinction, combined to change his mind. He saw evolution as a natural tendency to greater complexity and put forward four laws to explain how such complexity is brought about. The second law states that “the production of a new organ in an animal body results from a new need that continues to make itself felt,” and the fourth law, for which he is best remembered, states that such acquired characteristics are inherited. A much-quoted example of this view is the neck of the giraffe, which, through stretching for the uppermost leaves, becomes gradually elongated, and this adaptation is passed on to its offspring.

Today Lamarckism has largely been rejected in favor of Darwin's theory of evolution by natural selection, especially in the light of knowledge gained about genetic mutation as a source of the variation on which Darwin's theory is based. However, there have been strong advocates of Lamarck's theory, notably Luther Burbank, Paul Kammerer, and Trofim Lysenko. Some support for Lamarck's views comes with the interesting work of the immunologists Edward Steele and R.M. Gorczynski who claim to have shown that acquired immunological tolerance is inherited in mice.