LAMARCKISM, la-marlizm. The theory of organic evolution Which, in brief, accounts for the origin of life-forms by change of envi ronment, the exercise or use, and the disuse of organs, and the transmission of characteristics acquired during the lifetime of the individual. It differs from Darwinism in lacking the prin ciple of natural selection.
History of the Rise of the Theory.— Lamarck, in 1801, after 25 years' experience as a botanist, and when as a systematic zoologist he had devoted 10 years of labor in classifying the invertebrate animals of the Paris Museum, then the most extensive zoological collection in the world, published a lecture, delivered in 1800, in which he claimed that time without limit and favorable conditions of life are the two principal means or factors in the production of plants and animals. Under the head of favorable conditions he enumerates variations in climate, temperature, change of habits, varia tion in means of living, of preservation of life, of means of defense, and varying modes of reproduction. As the result of the action of these different agencies or factors, the faculties of animals, developed and strengthened by use, become diversified by the new habits so that by
degrees the new structures and organs thus arising become preserved and transmitted by heredity. Although Lamarck did not dis cover the principle of natural selection, he recognized the fact of competition, of a struggle for existence, but did not dwell on them to the extent that Darwin and later observers did. In 1802, 1803 and 1806 he reiterated and some what extended these views, which were pub lished in final form in 1809, in his
Lamarck's Factors of Organic Evolution. —These in their essential form are contained in his famous two laws: First Law.— In every animal which has not exceeded the term of its development, the more frequent and sustained use of any organ grad ually strengthens this organ, develops and en larges 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 imper ceptibly weakens it, causes it to become re duced, progressively diminishes its faculties and ends in its disappearance.
Second Law.— Everything which nature has caused individuals to acquire or lose by the influence of the circumstances to which their race may be for a long time exposed, and con sequently 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 (generation) and passes on to the new indi viduals which descend from it, provided that the changes thus acquired are common to both sexes, or to those which have given origin to these new individuals.
Lamarck also insisted that animals are modi fied in accordance with the diversity of their surroundings; that local causes, such as dif ferences in soil, climate, etc., give rise to varia tions and that the whole surface of the earth affords a diversity in localities and habits, one region differing from another, that though the environment remains the same for a long time and species remain constant for that period, yet there is a slow gradual change, and species are modified in adaptation to such changes. More over such changes induce alterations in the wants or needs of animals: this necessitates other movements or actions to satisfy the new needs, and hence they give origin to new habits, and this leads to the use or exercise of some organ or organs in a new direction, with the result that different parts or organs are modified in adaptation to the new surroundings and necessities of existence. All this is perfectly true. We now know that by geographical changes or from lack of food animals are com pelled to migrate into new regions, and are there obliged to adopt new habits and become transformed into new species or types. Thus whales have descended from terrestrial forms; the baleen whale has in its embryo stage rudi mentary teeth showing that it is a descendant of toothed whales. Lamarck refers to Geof frey's discovery in embryo birds of the groove where teeth should be situated, and subse quently fossil birds with teeth were unearthed.
The mole with its functionless eyes, due to underground life, the blind Proteus of Aus trian caves, the headless and eyeless bivalve mollusks, these parts lost by disuse; the evolu tion by atrophy of the limbs of the snake, due to their lack of use in passing through narrow places; wingless insects whose wings have been lost by disuse; the webs between the toes of ducks, geese, as well as those in the feet of the frogs, sea turtles, otter and beaver, are mentioned by Lamarck as examples of the effect of use and exercise. Other examples of use results are the origin of horns in ruminants; the long neck of the giraffe, which by the absence of herbage was obliged to browse on the foliage of trees °and to make continual effort to reach the shapes of the carniv ores, of the kangaroo and of the sloth which are accounted for by the necessity of their adopting new habits, and, by exercise in new directions, becoming adapted to the new condi tions of life. Although Lamarck gave few illustrations, it may be doubted whether any one has since his day more satisfactorily ex plained the origin of such forms or modifica tions. Lamarck also accounts for the origin of man, suggesting in a tentative way his rise from an arboreal or ape-like creature, with a de tailed hypothesis of the gradual process of his transformation, into a being with an upright posture, an enlarged brain, powers of reason and other human qualities. But besides these special cases Lamarck was broad and compre hensive in his views of nature and creation. He was the first to show that the animal series was not a continuous chain of being, but rather should be compared to a tree, with its branches. In fact he was the first to construct a gene alogical tree, the first attempt at a phylogeny of the animal world. He demanded unlimited time for the process of evolution. He antici pated the uniformitarian views of Lyell. He pointed out that where, as in Egypt, the cli matic conditions have remained the same for many centuries, species have remained constant, but that under a varying environment they become modified. He writes of the struggle for existence; shows that the stronger devour the weaker; he refers to the principle of com petition in the case of the sloth. He repeat edly insists on the fact that vestigial structures are the remains of organs which were actively used by the ancestors of existing forms. He shows, what is much insisted on at the present day, that change of functions in organs leads to their transformation or recreation, and that the assumption of new habits precede the origin of new, or the modification of organs already formed. A great deal is now said of the ef fects of migration and consequent geographical isolation in the origination of new species; Lamarck invoked this factor in the case of man, and he also pointed out the swamping effects of intercrossing. Lamarck's theory of use inheritance is denied by some, hut by others is regarded as an important factor in evolu tion. He does not, however, refer to the in heritance of mutilations, etc.
All these views lie at the foundation of the theory of organic evolution; yet Lamarck's opinions were set aside, misunderstood and ridiculed. Some crude and ungrounded hy potheses were mingled with them. In his time the sciences of palmontology, embryology and bionomics were undeveloped. Lamarck col lected but few facts, and he lacked the experi mental skill of Darwin; so that it was re served for the latter naturalist, half a century later, to convert the world to a belief in evolu tion. At present, however, it is acknowledged that Lamarckism affords the fundamental prin ciples on which rests the theory of organic evolution, and many of the most eminent natu ralists have worked and are working along Lamarckian lines.
Bibliography.— Packard, the Founder of Evolution: His Life and Work, with Translations of his Writings on Organic Evolution> (New York 1901) ; H. Elliot's trans lation of the Zoologiquc' (New York 1914); Spencer, H., 'Factors of Organic Evolution' (New York 1895) ; Cope, (The Pri mary Factors of Organic Evolution' (Chicago 1896); Hutton, and Lamarckism: Old and (London 1909).
ALPHEus S. PACKARD, Late Professor of Zoology, Brown University.