Another error which is committed in such cases is to neglect the influence of the maternal lineage. A common woman will lower the level of the offspring of a distinguished husband, and inversely. In his "History of Science and Scientists" Alphonse de Candolle has given irrefutable proof that the posterity of high-class men furnishes a great number proportionally of men high class in their turn, compared with that of the average population. This shows the value of the usual twaddle concerning this question. It is inconceivable that the laws of heredity should make an exception of the mental qualities of man. Moreover, the most deceptive point is the contrast of a man of genius with his children, who do not rise to his standard because they represent a combination of his ancestral energies with those of their mother. This contrast makes the children appear unfavorably, while the public has a general tendency to exaggerate the value of a great man.
The theory of the mneme throws light on this subject, by introducing a new factor in the question, that of ecphoria of the cerebral engrams of the ancestors, accumulated in the hereditary mneme.
Heredity of Acquired Characters.—While Darwin and Haeckel affirmed the possibility of the heredity of characters acquired during life by different tissues, for instance the brain, Weismann limits the possibility to everything that can modify the nucleoplasm of the germinal cells. We must first eliminate the question of the phenomena of blastophthoria, which we shall consider next, and which Weismann was, I think, the first to comprehend, without giving them the name.
On one hand we see the singular effects of castration, which we have already considered; on the other hand, an extraordinary constancy in the hereditary characters of the species. For more than three thousand six hundred years, which corresponds to about eight hundred generations, the Jews have been circumcised. Nevertheless, if a Jew ceases to circumcise his offspring the prepuce of his children grows as it did three thousand six hundred years ago, although, during the eight hundred generations in question, its absence from birth has prevented it reacting on the germinal cells of the individuals. If the engraphia of the external world could sensibly modify in a few generations the hereditary mneme of the species, it appears evident that the Jewish infants of the present day would be born without prepuce, or at least with an atrophied one.
It is on such facts, which are innumerable in natural history, that Weismann relies to repudiate absolutely the heredity of characters acquired by non-germinal organs and to attribute the development of organisms to blends and combinations due to conjugation, or crossing, as well as to natural selection, which he regards as all-powerful. Darwin well recognized the difficulty in question, and being unable to explain the facts, had recourse to the hypothesis of pangenesis, that is of small particles detached from all parts of the body and transported by the blood to the germinal cells, to transmit to them, for example, the qualities acquired by the brain during life. This hypothesis was so improbable that Darwin himself was forced to recognize it. Let us examine the facts.
On the one hand a newly born Chinese transported and brought up in France will learn French, and will show no inclination to learn or understand Chinese. This well-established fact seems in favor of Weismann and against the heredity of acquired characters. But, on the other hand, we cannot understand how the evolution of the brain and its functions takes place, without admitting that in one way or another the characters acquired by habits repeated during many generations gradually accumulate in the form of hereditary dispositions in the germinal protoplasm. It is certain that our brain has progressed since the time when our ancestors were similar to the gorilla, or even the cave man at the beginning of the quaternary age. How can this cerebral progression be explained only by selection which can only eliminate, and by crossings which by themselves can hardly raise the average? It is here that the intervention of an unknown power is necessary, something unexplained, the action of which has been lately recorded in the phenomena of mutations of de Vries.
De Vries proves that certain variations appear suddenly and without any known cause, and have a much greater tendency to be preserved than the variations obtained by crossing and selection. In my opinion the phenomena of the mneme revealed by Hering and Semon explain the apparent contradictions which have hitherto impaired the theories of heredity. Mnemic engraphy explains, by its infinitesimal and repeated action through numerous generations, how the external world may little by little transmit to the germinal cells the characters which it impresses on organisms. The eight hundred generations during which the prepuce of the Jews has been cut off have not yet sufficed for the ecphoria of the corresponding negative mnemic engraphia; while conjugation and selection modify rapidly and strongly in a few generations; a fact which is more striking and allows of direct experiment. Moreover, a positive engraphia must necessarily act more powerfully, and it seems to me that mutations must be the ecphoria of accumulated former latent engraphias.
Merrifield and Standfuss, by exposing caterpillars and chrysalids for varying periods to considerable degrees of cold and heat, have determined permanent changes in the specific characters of the butterflies which have emerged from them.
Standfuss and Fischer have also shown that, after several generations, by continuing the action of cold on the caterpillars, the variations thus produced can be preserved even after the cold has ceased to act. No doubt the cold acts on the germinal cells as on the rest of the body, but the heredity of an acquired character is thus demonstrated.
The experiments of Miss de Chauvin on salamanders (Axolotl) are still more conclusive, for we are dealing here with characters acquired through aquatic or aërial media, which can hardly act on the sexual glands. We cannot continue this subject any further and we return to the work of Semon. It is needless to say that the nature of mnemic engraphia remains itself an unknown quantity. As long as we are unable to transform inert matter into a living organism we shall remain in ignorance. But, when it is accepted with the laws of the phenomena which it produces, this unknown quantity, as Semon has shown, alone suffices to explain all the rest, and is already a great step toward the comprehension of the laws which govern life.