LAMARCKISM. The doctrine often spoken of as Lamarck ism is only a part of Lamarck's teaching concerning the transfor mation of lower into higher forms of life, and probably not the most important part. Lamarck incorporated into his theory of transformation (organic evolution) a belief that had been current in many lands as long as we have records, written and oral, and is still ardently adhered to even by many animal breeders. In the folk-lore of primitive peoples there are stories that take for granted that acquired characters are inherited. These stories now appeal to our sense of humour and would have long ago been forgotten or disregarded by scientists were it not that in every generation new illustrations are continually brought forward. Much of this evidence rests on hearsay, and much of it arises from a succession of events that is merely fortuitous.
An acquired character may be defined as one that has developed in the course of the life of an individual in the somatic or body cells, usually as a direct response to some external change in the environment or through the use or disuse of a part. The inheri tance of such a character means its reappearance in one or more individuals in the next or in succeeding generations. For example, the human skin turns brown on exposure to sunlight. If this acquired character were transmissible, the children from two tanned persons (or even from one of them, perhaps) should have a darker skin than that characteristic of the white race to which the parents belonged. Whether it is to be expected that the chil dren should be as dark as their sun-tanned parents, or only some what darker than the average of the white race, as some Lamarck ians suggest, is a matter of choice. There is no evidence that such transmission occurs even although it is evident that the darker skinned races of man are found in tropical and subtropical parts of the earth. A somewhat different example would be found in the supposed inheritance of a change brought about by the use and disuse of a special organ. The blacksmith's arm (or any other set of muscles) enlarges when used continually against an external resistance such as the weight of the hammer. If the effect were inherited, his children at birth would have unusually large arms; if not at birth, then, when they become adults, even although they had not used their arms excessively. There is no evidence support ing this case. A more subtle illustration is found in the supposed inheritance of an increased dexterity of the hands of a musician through practice ; the skill acquired, although causing no visible increase in size of the fingers, might be imagined to be inherited by his children, and they might then be expected to play skilfully on the piano without practice; or if this seems too ridiculous, they might be imagined to learn more rapidly than did one of their parents. Just how the intricate interplay of cerebral sequences that
has given the dexterity to the musician's fingers could ever be transferred to a spermatozoon, and through it to his children, has never been brought within the range of biological possibilities. It is clear that the fact of a musician's children playing the piano well might just as well be due to parent and offspring both inherit ing unusual musical aptitude, quite apart from practice.
Lamarck recognized several ways in which the environment brings about changes in plants and animals, and it is significant to note that his attention was directed more particularly to the adaptive character of the response, which, as Bergson points out, implies the teleological nature of the result. In plants the response is direct and immediate, i.e., not through the mediation of a cen tral nervous reaction system, since this is absent in plants. In ani mals the adaptive changes are supposed to be more indirect. According to Lamarck, new needs (besoins) arise in animals as a result of a change in the environment. This leads to new types of behaviour involving new uses of pre-existing organs. Their use leads to an increase in size or to other methods of functioning. Conversely, the disuse of other parts leads to their decline. It is the resulting material alterations that are inherited. The examples that Lamarck gives to illustrate his doctrine are illuminating. If seeds of a plant adapted to live in a bog should be carried to a neighbouring hill and germinate there, they become adapted to the drier soil of the hill and change their character ; the new type perpetuates itself and may be transformed into a new species. In animals, as stated above, a new environment calls forth new needs and the animal seeks to satisfy them by making some effort. Thus new needs engender new habits which modify the parts. The effects are inherited. For example, the giraffe, seeking to browse higher and higher on the leaves of trees on which it feeds, stretches its neck; as a result of this habit, continued for a long time in all the individuals of the race, the giraffe's front limbs and neck have gradually grown longer. Birds that need to rest on the water to find their food, spread out their feet when they wish to swim. The skin becomes accustomed to being stretched and forms the web between the toes. The horns of ruminants have resulted from their butting their heads together during combats. Flat-fishes have arisen from the habit of turning on one side in shallow water; the eye on the lower side has moved towards the upper side as a result of the need of paying attention to objects above the fish. These naïve examples constitute the evidence on which Lamarck rested his theory.