LAMARCK, JEAN BAPTISTE PIERRE ANTOINE DE MONET, CHEVALIER DE (1744-1829), French naturalist, was born on Aug. I, 1744, at Bazantin, Picardy, the son of the lord of the manor. He studied under the Jesuits at Amiens, but when 17, joined the troops at Bergen-op-Zoom, where for his bravery he was given a commission. After the peace he went to Paris to study medicine, supporting himself by working in a banker's office. He became interested in meteorology and in chemical speculations but threw his main strength into botany. In 1778 he published his Flore francaise, a work which by a dichoto mous system of characters enabled the student to determine species with facility. This gained for its author admission to the Academy of Sciences.
In 1781 and 1782, under the title of botanist to the king, he travelled across Europe and on his return wrote the Dictionnaire de Botanique and the Illustrations de Genres, voluminous works contributed to the Encyclopedie Methodique (1785). In 1793, in consequence of changes in organization at the Jardin du Roi, where he had held a botanical appointment since 1788, Lamarck was presented to a zoological chair, and called to lecture on the Insecta and Vermes of Linnaeus, the animals for which he intro duced the term Invertebrata. The first expression of his views on evolution given in his Systeme des Animaux sans V ertebres (18o1) and Recherches sur l'Organisation des Corps Vivans (1802) were elaborated in his Philosophie Zoologique (1809) ; and in spite of impaired sight, he published the Histoire naturelle des animaux sans vertebres (1815-22) with the assistance, in the last two volumes, of his eldest daughter and of P. A. Latreille (1762-1833). He died on Dec. 18, 1829.
As a naturalist Lamarck excelled in width of scope, fertility of ideas and a faculty of precise description. The work which con stitutes his claim to the highest honour as a zoologist is his de tailed investigation of living and fossil Invertebrata. His en deavours at classification of such groups as the echinoderms, ascidians and intestinal worms are necessarily very defective, yet they are not without interest, on account of the attempt to unite in one great division as Articulata all those groups that appeared to present a segmented construction. He was the first to distin guish vertebrate from invertebrate animals by the presence of a vertebral column, and among the Invertebrate to found the groups Crustacea, Arachnida and Annelida. In i 785 he evinced his appre
ciation of the necessity of natural orders in botany by a some what crude attempt at the classification of plants.
To the general reader Lamarck is chiefly interesting for his theory of the origin of the diversities of animal forms. The idea, favoured by Buffon before him, that species were not un alterable, and that the more complex were developed from pre existent simpler forms, was widely propagated by Lamarck. Spontaneous generation, he considered, might have resulted from heat and electricity causing in small gelatinous bodies an utricular structure, and inducing a "singular tension," a kind of "erethisme" or "orgasme." Having thus accounted for the appearance of life, he explained the whole organization of animals and formation of different organs by four laws (introduction to his Histoire naturelle des animaux sans vertebres, 1815) : I. Life by its proper forces tends continually to increase the volume of every body possessing it, and to enlarge its parts, up to a limit which it brings about.
2. The production of a new organ in an animal body results from the supervention of a new want continuing to make itself felt, and a new movement which this want gives birth to and encourages.
3. The development of organs and their force of action are con stantly in ratio to the employment of these organs.
4. All which has been acquired, laid down, or changed in the organization of individuals in the course of their life is conserved by generation and transmitted to the new individuals which proceed from those which have undergone those changes.
The second law is of ten referred to as Lamarck's hypothesis of the evolution of organs in animals by appetence or longing, al though he does not teach that the animal's desires affect its con formation directly, but that altered wants lead to altered habits, which result in the formation of new organs as well as in modi fication. (See LAMARCKISM.) The fourth law expresses the in heritance of acquired characters. (See EVOLUTION.) See A. S. Packard, Lamarck, the Founder of Evolution (19o1 with bibliography) ; G. Revault d'Allonnes, Lamarck (Paris, 1910) ; E. Perrier, Lamarck (Paris, 1925) and H. Daudin, Cuvier et Lamarck; Les Classes Zoologiques et l'idee de sine animale (1926).