Lamarck is usually remembered today mainly in connection with a discredited theory of heredity, the "inheritance of acquired traits," but Charles Darwin and others acknowledged him as an early exponent of ideas about evolution. In 1861, for example, Darwin wrote:
"Lamarck was the first man whose conclusions on the subject excited much attention. This justly celebrated naturalist first published his views in 1801. . . he first did the eminent service of arousing attention to the probability of all changes in the organic, as well as in the inorganic world, being the result of law, and not of miraculous interposition."
Lamarck's own theory of evolution was in fact based on the idea that individuals adapt during their own lifetimes and transmit traits they acquire to their offspring. Offspring then adapt from where the parents left off, enabling evolution to advance. As a mechanism for adaptation, Lamarck proposed that individuals increased specific capabilities by exercising them, while losing others through disuse. While this conception of evolution did not originate wholely with Lamarck, he has come to personify pre-Darwinian ideas about biological evolution, now called Lamarckism.
Born into poor nobility (hence 'chevalier'), Lamarck served in the army before becoming interested in natural history and writing a multi-volume flora of France. This caught the attention of Le Comte de Buffon who arranged for him to be appointed to the Musée d'Histoire Naturelle in Paris.
After years working on plants, Lamarck was appointed curator of invertebrates -- another term he coined. He began a series of public lectures. Before 1800, he was an essentialist who believed species were unchanging. After working on the molluscs of the Paris Basin, he grew convinced that transmutation or change in the nature of a species occurred over time. He set out to develop an explanation, which he outlined in his 1809 work, Philosophie Zoologique.
Lamarck developed two laws:
His defenders believe he is unfairly vilified today. They note that he believed in organic evolution at a time when there was no theoretical framework to explain evolution. He also argued that function precedes form, an issue of some contention among evolutionary theorists at the time. On the other hand, the inheritance of acquired characteristics is now widely refuted. August Weismann disproved the theory by cutting the tails off mice, demonstrating that the injury was not passed on to the offspring. Jews and other religious groups have been circumcising men for hundreds of generations with no noticeable withering of the foreskin among their descendants. However, Lamarck did not count injury or mutilation as a true acquired characteristic, only those which were initiated by the animal's own needs were deemed to be passed on.
Nowadays, the idea of passing on to offspring characteristics that were acquired during an organism's lifetime is called Lamarckian. This view was, until very recently, thought to be completely inconsistent with modern genetics, but recent discoveries, as discussed in the article on epigenetic inheritance, show that this is not quite the case. So there may be room for some sort of Lamarckian evolution after all.
Darwin not only praised Lamarck in the third edition of The Origin of Species for supporting the concept of evolution and bringing it to the attention of others, but also accepted the idea of use and disuse, and developed his theory of pangenesis partially to explain its apparent occurrence. Darwin and many contemporaries also believed in the inheritance of acquired characteristics, an idea that was much more plausible before the discovery of the cellular mechanisms for genetic transmission. (Darwin, incidentally, acknowledged his theory would remain somewhat incomplete if the mechanism for inheritance could not be discovered.)
See also: Lysenko
¹ For a discussion of linguistic priority, see Biology.