changes; and even if the cause of the variation ia of a psychological nature, we can hardly call it an effort, unless we give a very unusual extension to the meaning of the word. The truth is, it is necessary to dig beneath the effort itself and look for a deeper cause.
This is especially necessar>', we believe, if we wish to get at a cause of regular hereditary variations. We are not going to enter here into the controversies over the transmissibility of acquired characters; still less do we wish to take too definite a side on thiB question, which is not within our province. But we cannot remain com- pletely indifferent to it. Nowhere is it clearer that phi- losophers can not to-day content themeelvcs with vague generalities, but nmst follow the scientists in experimental detail and discuss the results with them. If Spencer had begun by putting to himself the question of the heredita- bility of acquired characters, his evolutionism would no doubt have taken an altogether different form. If (as seems probable to us) a habit contracted by the individual were transmitted to its descendants only in very exceptional cases, all the Spencerian psychology would need re-:iiaking, and a large part of Spencer's philosophy would fall to pieces. Let us say, then, how the problem seems to us to present itself, and in what direction an attempt might be made to solve it.
After having been affirmed as a dc^ma, the trans- missibility of acquired characters has been no less dog- matically denied, for reasons drawn a priori from the supposed nature of germinal cells. It is well known how Weismann was led, by his hypothesis of the continuity of the gcrni-plasm, to regard the germinal cells — ova and spermatozoa^as almost independent of the somatic cells. Starting from this, it has been claimed, and is still claimed by many, that the hereditary transmission of an acquired
I-l
Edity
character is inconceivable. But if, perchance, experiment should show that acquired character are transmissible, it would prove thereby that the germ-plasm is not so independent of the somatic envelope as has been contended, and the transmissibility of acquired characters would become ipso facto conceivable; which amounts to saying that coneeivability and inconceivability have nothing to do with the case, and that experience alone must settle the matter. But it is just here that the difficulty begins. The acquired characters we are speaking of are generally habits or the effects of habit, and at the root of most habits there is a natural disposition. So that one can always ask whether it is really the habit acquired by the soma of the individual that is tran'^mitted, or whether it is not rather a natural aptitude, which existed prior to the habit. This aptitude would have remained inherent in the germ- plasm which the individual bears within him, as it was in the individual himself and consequently in the germ whence he sprang. Thus, for instance, there is no proof that the mole has become blind because it has formed the habit of living underground; it is perhaps because its eyes were becoming atrophied that it condemned itself to a life underground.! If this is the case, the tendency to lose the power of vision has been transmitted from germ to germ without anything being acquired or lost by the soma of the mole itself. From tbe fact that the son of a fencing-master has become a good fencer much more quickly than his father, we cannot infer that the habit of the parent has been transmitted to the child; for certain natural dispositions in course of growth may have passed from the plasma engendering the father to the plasma engendering
1 Cu^mt, "La Nouvelle ThSorie transform iete" ^Revue gtnfrale des teieneet, 1894). Cf. dbrgail. Evolution and Adaplatunt, London, 1003, p. 367.
80 Creative Evolution
the son, may have grown on the way by the effect of the primitive impetus, and thus assured to the son a greater suppleness than the father had, without troubling, so to speak, about what the father did. So of many examples drawn from the progressive domestication of animals: it is hard to say whether it is the acquired habit that is transmitted or only a certain natural tendency — that, indeed, which has caused such and such a particular species or certain of its representatives to be specially chosen for domestication. The truth is, when every doubtful case, every fact open to more than one inter- pretation, has been eliminated, there remains hardly a single unquestionable example of acquired and trans- mitted peculiarities, beyond the famous experiments of Brown-S^uard, repeated and confirmed by other physiologists." By cutting the spinal cord or the sciatic nerve of guinea-pigs, Brown-S^uard brought about an epileptic state which was transmitted to the descendants. Lesions of the same sciatic nerve, of the restiform body, etc., provoked various troubles in the guinea-pig which its progeny inherited sometimes in a quite different form: exophthalmia, loss of toes, etc. But it is not demonstrated that in these different cases of hereditary transmission there had been a real influence of the soma of the animal on itfl germ-plasm. Weismann at once objected that the operations of Brown-S6quard might have introduced cer- tain special microbes into the body of the guinea-pig, which had found their means of nutrition in the nervous tissues and transmitted the malady by penetrating into the sexual elements.' This objection has been answered
' Brown-S&iuanl, ' ' Nouvelles recherches sur I'^piiepeie due k certainea IMons de la moelle £pini£ero et des nerfa rachidiens'' (Areh. de phyti- olagie, vol. ii-, 1866, pp. 211, 422. and 497).
' WdBmuiin, Aufsalze Hiier VrrerbuT^g. Jena, 1892, pp. 378-378, and also VortTiige librr DeKxndenztkeorie, Jena, 100? voL ii., p. 76.
^B by Brown-Sequard himself;' but a more plausible one ^P cught be raised. Some experiments of Voisin and Peron ^B have shown that fits of epilepsy are followed by the elimi- ^B nation of a toxic body which, when injected into animals,' ^P is capable of producing convulsive symptoms. Perhaps ^P the trophic disorders following the nerve lesions made by ^P Brown-S^quard correspond to the formation of precisely this con\'ulsion-causing poison. If so, the toxin passed from the guinea-pig to its spermatozoon or ovum, and caused in the development of the embryo a general dis- turbance, which, however, had no \'isible effects except at one point or another of the organism when developed.
I In that case, what occurred would have been somewhat tht same as in the experiments of Chanin, Delamare, and Moussu, where guinea-pigs in gestation, whose liver or kidney was injured, transmitted the lesion to their progeny, simply because the injury to the mother's organ had given rise to specific "cytotoxins" which acted on the corresponding organ of the foetus.* It is true that, in these experiments, as in a former observation of the same physiologists,' it was the already formed foetus that was inSuenced by the toxins. But other researches of Charrin have resulted in showing that the same effect may be pro- duced, by an analogous process, on the spermatozoa and the ova.' To conclude, then: the inheritance of an ac- Brown-SA^uard, "H^rSdiW d'une affection due i une cause acd- denlelle" {Arch, de phyaiologie, 1892, pp. 686 ff.).
>* Voiain and Peron, "Recherchea sur la toxicity urinaire chOE lea ^fnleotiques" (Arch, de neurologie, vol. udv., 1892, and xxv., 1893. Cf. the work ot Voisin, L'tpUepde, Paris, 1897, pp. 125-133). • Chamn, Delamare and Housau. " TranamiBirion expfrimentale auit deMeadantadelteionsd^velopp^chezlea aacendants" {C.R. del' Acad. de* Kienca, vol. cxxxv., 1902, p. 191). Cf. Morgan, Evolution and Adapbaion, p. 257, and E)eluge. L'HiridiU, 2nd edition, p. 38S.
' Charrin and Delamare, "H£rMit£ ceUulaire" (C. R. de I'Aead. da teienett, vol. OTXxiii., 1901, pp. 69-71). • Charrin, "L'H^rfidiuS pathologique" {Revue ginirale de» tcUncet,
82 CREATIVE EVOLUTION ichap.
quired peculiarity in the experiments of Brown-S^quard can be explained by the effect of a toxin on the germ. The lesion, however well localized it seems, is transmitted by the same process as, for instance, the taint of alcoholism. But may it not be the same in the case of every acquired peculiarity that has become hereditary?
There is, indeed, one point on which both those who affirm and those who deny the transmissibility of acquired characters are agreed, namely, that certain influences, such as that of alcohol, can affect at the same time both the living being and the germ-plasm it contains. In such ease, there is inheritance of a defect, and the result is OS if the soma of the parent had acted on the germ-plasm, although in reality soma and plasma have simply both suffered the action of the same cause. Now, suppose that the soma can influence the germ-plasm, as those believe who hold that acquired characters are trans- missible. Is not the most natural hypothesis to suppose that things happen in this second case as in the first, and that the direct effect of the influence of the soma is a general alteration of the germ-plasm? If this is the cast;, it is by exception, and in some sort by accident, that the modification of the descendant is the same as that of the parent. It is like the hereditability of the alcoholic taint: it passes from father to children, but it may take a different form in each child, and in none of them be like what it was in the father. Let the letter C represent the change in the plasm, C being either positive or negative, that is to say, showing either the gain or loss of certain substances. The effect will not be an exact reproduction of the cause, nor will the change in the germ-plasm, provoked by a cer- tain modification of a certain part of the soma, deterraiDC a similar modification of the corresponding part of the new oi^anism in process of formation, unless all the other
nascent parts of this organism enjoy a kind of immunity
as regards C: the same part will then undergo alteration
in the new organism, because it happens that the develop-
ment of this part is alone subject to the new influence.
And, even then, the part might be altered in an entirely
different way from that in wMch the corresponding part-
was altered in the generating organism.
We should propose, then, to introduce a distinction between the hereditability of deination and that of ckar- adfr. An individual which acquires a new character thereby demotes from the form it previously had, which form the germs, or oftener the half-germs, it contains would have reproduced in their development. If this modification does not involve the production of sub- stances capable of changing the germ-plasm, or does not so affect nutrition as to deprive the germ-plasm of certain of its clement^;, it will have no effect on the offspring of the individual. This is probably the case as a rule. If, on the contrary, it has some effect, this is likely to be due to a chemical change which it has induced in the germ- plasm. This chemical change might, by exception, bring about the original modification again in the organism which the germ is about to develop, but there are as many and more chances that it will do something else. In this latter case, the generated organism will perhaps deviate from the normr-J type as much as the generating organism, but it will do so differently. It will have inherited deviation and not character. In general, therefore, the habits formed by an individual have probably no echo in its offspring; and when they have, the modification in the descendants may have no visible hkeness to the original one. Such, at least, is the hypothesis which seems to us most likely, In any case, in default of proof to the con- trary, and so long as the decisive experiments called for
(OHAP.
by an eminent biologist' have not been made, we must keep to the actual results of observation. Now, even if we take the most favorable view of the theory of the trana- missibility of acquired characters, and assume that the ostensible acquired character is not, in moat cases, the more or less tardy development of an innate character, facts show us that hereditary transmission is the excep- tion and not the rule. How, then, shall we expect it to develop an organ such as the eye? When we think of the enormous number of variations, all in the same direction, that we must suppose to be accumulated before the passage from the pigment-spot of the Infusorian to the eye of the mollusc and of the vertebrate is possible, we do not see how heredity, as we observe it, could ever have determined this piling-up of differences, even sup- posing that individual efforts could have produced each of them singly. That is to say that neo-Lamarckism is no more able than any other form of evolutionism to solve the problem.