LAMARCK, JEAN BAPTISTE PIERRE ANTOINE DE MONET DE (b. Bazentin-le-Petit, Picardy, France, 1 August 1744; d. Paris, France, 28 December 1829), botany, invertebrate zoology and paleontology, evolution.

Lamarck has been credited with introducing a branching family tree into evolutionary theory. It is true that in his major evolutionary works he often spoke of branchings below the level of the “masses,” but he regarded these branchings as exceptions to the general rule of increasing structural complexity. In the Philosophie zoologique, Lamarck argued for a unilinear series of classes in each kingdom. In an addition at the end of the work, however, he presented a branching arrangement for animal classes in what is now a well-known diagram. It is significant that he was never able to integrate this new order with his evolutionary theory. The same discontinuity occurs in the 1815 “Introduction”; in the body of the work he assume a linear series of the “masses,” and in a supplement he presents a diagram of branching classes (different from the 1809 version) which he labels as the presumed order of formation. These evolutionary trees were Lamarck's acknowledgment of advances in comparative anatomy and natural classification. That he could not include them with his two-factor theory shows his strong lifelong commitment to a philosophical idea: the chain of being and its modified version of a hierarchical unilinear series of classes in the two kingdoms.

The above example indicates a very important aspect of Lamarck's evolutionary theories. They were put forth by a philosopher-naturalist and not a positivist scientist. From his earliest scientific work, Lamarck was always more interested in the broad picture of nature and in general interrelations than in the details. While he did give scattered examples to support his theories, he was never systematic, always promising more evidence in a forthcoming work and never producing it. Lamarck felt that his theories were so obvious that they did not need extensive proof. In addition he was paranoid with respect to the French scientific community because of their attitudes toward his work in chemistry; he was convinced that he never could win over his enemies, so he did not try. With all his work in botany and invertebrate zoology, he would have had abundant examples if he had wanted them. He always separated his theories and his detailed classificatory work. Although he spent years carefully determining, describing, and classifying species, in his evolutionary views he maintained that species were almost irrelevant, exceptions to the general natural law of evolution.

Origins of Lamarck's Theory.

Lamarck was fifty-five when, in 1800, he made his first public statement of evolution. Until the late 1790's he had believed in the fixity of species. Thus the question has always been why he changed his mind. Various answers have been and still are being put forth. They range from different influences from his own work to the particular influence of individuals. Among the former explanations, Lamarck's work in geology, invertebrate classification, paleontology and the problem of extinction, and chemistry have all been seen as the crucial factor. Individuals who have been held to have exerted the decisive influence on Lamarck's change of mind include Lacépède, Cabanis, Cuvier, and such earlier speculative thinkers as Buffon, Diderot, De Maillet, and Robinet. A study of the origins of Lamarck's theory of evolution must be broadened beyond the issue of the fixity of species. He also changed his views on other issues. Not only should we look at the changes, but we should also look at the continuities. Many aspects of Lamarck's evolutionary theory are found in his earlier works in different fields; some components of the theory, however, are new. Burkhardt, who recognizes the importance of continuities, has recently studied certain factors which he thinks were the immediate causes of Lamarck's evolutionary thought. In an article (1972) he presents a convincing argument to show that Lamarck changed his views on two important subjects (spontaneous generation and the mutability of species) between the spring of 1799 and the spring of 1800 and that in both cases the changes came about as a result of confronting the question of extinction. In the section on invertebrate paleontology, we summarized Burkhardt's position. Lamarck was faced with the extinction question in his study of fossil shells. Since an acceptance of extinction would have violated his view of nature, and since the migration theory was not really a satisfactory explanation, Lamarck was left with the choice that species change gradually with time.

Lamarck's acceptance of the possibility of spontaneous generation came via a more circuitous route but one which was also related to the study of invertebrates and to the extinction question. Burkhardt suggests that Lamarck's study of the invertebrates led him to a new definition of life. For Lamarck, the simplest organism demonstrated the minimum conditions necessary for life; lacking any specialized organs, they depended entirely on the movement of subtle fluids in the environment to maintain their organic movements. The next logical step was to move to a belief in spontaneous generation. If the subtle fluids could maintain this simple form of life, why could they not also create it when the circumstances were right? The extinction issue came in when Lamarck realized that these organisms were killed in bad weather. The only way he could account for their reappearance was by spontaneous generation. A belief in spontaneous generation was necessary for a theory of evolution, unless one wished to invoke a