Lamarck versus Weismann

Abstract

I HAD not intended to reply to Mr. Cunningham's criticism of a passage in my book which he thinks is pure Lamarckism (see NATURE, July 25, p. 297); but now that Prof. Ray Lankester adopts the same view, I will make a few remarks upon the case. Mr. Cunningham italicizes the words, “the constant repetition of this effort causes the eye gradually to move round the head till it comes to the upper side,” and claims this as a Lamarckian explanation. But if we italicize the following words, which occur three lines further on, “those usually surviving whose eyes retained more and more of the position into which the young fish tried to twist them,” we shall see that the survival of favourable variations is, even here, the real cause at work. For the transference of the eye to the upper side was a useful change—perhaps, under the peculiar conditions of existence and development—an absolutely essential one. The amount to which the eye could be twisted and retained in its new position was variable, as all other such characters are variable. Those individuals who had this faculty in the greatest degree were among those that survived, and. it is not at all necessary to assume that any portion of the change due solely to the effort was inherited, but only that those individuals which were the most favourably constituted in this respect transmitted their peculiar constitution to their offspring, and thus the twisting would take place earlier and earlier in the development of the individual Even Darwin himself, who believed in the heredity of acquired variations, says that “the tendency to distortion would no doubt be increased through the principle of inberitance”; and this is really all that is necessary. In most of the higher animals symmetrical development of the two sides of the body is of vital importance, and is strictly preserved by natural selection; but more or less defect of symmetry often occurs as a variation or monstrosity, and in cases where such asymmetry was useful these variations would be preserved and increased by selection and heredity. An altogether erroneous view is taken of the fact of effort being used in this case, as if it were something unusual. But in all cases selection produces changes which are useful and whose use is often indicated by effort. The giraffe uses effort in stretching its neck to obtain food during a drought; the antelope exerts itself to the utmost to escape from the leopard; but it is now recognized that it is not the individual change produced by this effort that is inherited, but the favourable constitution which renders extreme effort unnecessary, and causes its possessors to survive while those less favourably constituted, and who therefore have to use greater effort, succumb. In the case of the developing flat-fish also, the effort indicated the direction of the useful modification, and any variations tending either to the right kind of asymmetry or to a mobility of the eye, admitting its being twisted and retained in its new position, during the growth of the individual, would be certainly preserved.