(5) Lamarck's characteristic doctrine is the inheritance of characters acquired during the life time of the individual. (See UsE-IxtiflifTsNcE.) This by some writers is regarded as if the only feature of Lamarckism. hut in reality he discusses the subject very briefly. yet it appears to be a necessary result of the action of use and disuse, and of change of any of the conditions of life.
(6) The effects of crossing were considered by Laniard:, rind—what been overlooked by commentators and eritics—he (dearly insists on the leveling or swamping effects of free inter crossino. Ile anticipated much modern discussion in his statement: "If. when any peculiarities of form or any defects whatsoever are acquired, the individuals in this case always pairing. they will reproduce the same peculiarities, and if for successive generations confined to such unions, a special and distinct race will then be formed.
But perpetual crosses between individuals which have not the same peculiarities of form result in the disappearance of all time peculiarities ac quired by particular circumstances." (7) The principle of geographical isolation (see ISOLATION) NV:Is anticipated by Lamarck, who, at the close of the paragraph above quoted, goes un to say: "Were not men separated by dis tances of habitation, the mixtures resulting from ossing would obliterate the general characters which distinguish different nations." (Philo sophic zoOlogique, p. 262.) This idea of segre gation is also involved in his account of the origin of man from apes. lie does not, however, specifically apply this principle to other animals than La niarck ( Ph ilosoph ic zoologique, 1809) sum med up his conclusions in the following laws: "Pirst Law.—.In every animal which has not exceeded the term of its development, the more frequent and sustained use of any organ gradual ly strengthens this organ. develops and enlarges it, and gives it a strength proportioned to the length of time of such use; while the constant lack of use of such an organ imperceptibly weak ens it, causes it to become reduced, progressively diminishes its faculties, and ends in its disap pearance.
";._treond Law.—Uverything which nature has caused individuals to acquire or lose by the in fluence of the circumstances to which their race limy he for a long time exposed, and consequently by the influence of the predominant use of such an organ, or by that of the constant lack of use of such part, it preserves by heredity (w.'nern ilea) and passes on to the new individuals which descend from it, provided that the changes thus required are common to both sexes, or to those which have given origin to these new individ uals." Afterwards in time introduction to the A ?and/us sans rerted.tres (1815) he enunciates these prin ciples under four laws, as follows: "First Lame—Life, by its proper forces, con tinually tends to increase the volume of every body which possesses it, and to increase the size of its parts, up to a limit which it brings about.
"Second Laic.—The production of a organ in an animal body results from the supervention of a new want (besoin) which continues to make itself felt, and of a new movement which this want gives rise to and maintains.
"Third Law.—The development of organs and their power of action are constantly in ratio to the employment of these organs.
"Fourth Lair.—Everything which has been ac quired, impressed upon. or elmnged in the or ganization of individuals, during the course of their life is preserved by generation, and trans mitted to the new individuals whieh have de scended from those which have undergone those change." Lamarck failed to eateh the idea of natural selection—the essence of Dar•inism—though his views on overpopulation were fundamentally like those of Malthus (I79S). whose essay on population gave the hint both to Darwin and to Wallace, which became the germ of the theory of natural selection (q.v.). See EVOLUTION.