Pangenesis Improbable
The more important and best-known phenomena of heredity do not require any such hypothesis, and leading facts (such as atavism, transmission of lost parts, and the general non-transmission of acquired characters) are so adverse to it that Darwin has to concede that many of the reproductive gemmules are atavistic, and that by continuous self-multiplication they may preserve a practical “continuity of germ-substance,” as Weismann would term it. The idea that the relationship of offspring to parent is one of direct descent is, as Galton tells us, “wholly untenable”; and the only reason he admits some supplementary traces of pangenesis into his “Theory of Heredity,”71 is that he may thus account for the more or less questionable cases of the transmission of acquired characters. But there appears to be no necessity even for this concession. We ought therefore to dispense with the useless and gratuitous hypothesis that cells multiply by throwing off minute self-multiplying gemmules, as well as by the well-known method of self-division. If pangenesis occurs, the transmission of acquired characters ought to be a prominent fact. The size, strength, health and other good or evil qualities of the cells could hardly fail to exercise a marked and corresponding effect upon the size and quality of the reproductive gemmules thrown off by those cells. The direct evidence tends to show that these free gemmules do not exist. Transfusion of blood has failed to affect inheritance in the slightest degree. Pangenesis, with its attraction of gemmules from all parts of the body into the germ-cells, and the free circulation of gemmules in the offspring till they hit upon or are attracted by the particular cell or cells, with which alone they can readily unite, seems a less feasible theory and less in conformity with the whole of the facts than an hypothesis of germ-continuity which supposes that the development of the germ-plasm and of the successive self-dividing cells of the body proceeds from within. Darwin’s keen analogy of the fertilization of plants by pollen renders development from without conceivable, but as there are no insects to convey gemmules to their destination, each kind of gemmule would have to be exceedingly numerous and easily attracted from amongst an inconceivable number of other gemmules. Arguments against pangenesis can also be drawn from the case of neuter insects—a fact which seems to have escaped Darwin’s notice, although he had seen how strongly that case was opposed to the doctrine which is the essential basis of the theory of pangenesis.