The Inheritance of Acquired Characters

Abstract

IT would be difficult to overrate the importance of the instance given by my friend Prof. Hartog in the last number of NATURE (p. 462) of the inheritance of a character acquired by habit; but the explanation which he offers of the non-inheritance of characters produced by mutilation, so far from being flat Lamarckism, appears to me to flavour of ultra-Darwinism, and the following hypothesis, resting more directly on mechanical principles, might be suggested. It is well known that many of the lower animals possess a remarkable power of regenerating lost parts. The garden snail offers a familiar instance: if the eyes be snipped off from their tentacles, they are in a short time reproduced, usually with a structure as perfect as that of their predecessors, as may be proved by a histological examination of thin slices. This power appears to be possessed to an unlimited extent, for one of my former pupils, Mr. Trevor Evans, performed the experiment twenty times in succession on the same snail, and the last eye was as perfect as the first; he then relinquished the research, being persuaded that the power of regeneration would only terminate with the life of the unfortunate subject. This power of growing afresh so complex and specialized an organ as an eye is certainly at first sight not a little astonishing, but it appears to be capable of a very simple explanation: the cells terminating the cut stump of the tentacle are the ancestors of those which were removed; a fresh series of descendants are derived from them, similarly related to the ancestral cells as their predecessors which they replace; the first generation of descendants become in turn ancestors to a second generation, similarly related to them as were the second tier of extirpated cells; and this process of descent being repeated, the completed organ will at length be rebuilt. The possibility of this arises from the fact that in the snail the embryological course of development is capable of being repeated by the adult structure. In higher organisms this possibility does not as a rule exist, and mutilation is not followed by regeneration; but even in their case the ancestral cells remain, and when the embryological development is repeated their representatives in the embryo are present to give rise to descendants of the normal type in the normal fashion. It follows from this view, which leaves pangenesis out of account, that mutilations cannot possibly be inherited, and this for the reason that the cells forming the organism at each stage of its development must be regarded as the ancestors of those of the next stage; thus finally we are brought round to something which looks very like Weismannism.