It is not my intention to discuss these questions in detail; they are too many-sided and of too much importance to be treated of merely in passing; moreover, I gave expression years ago to my views on this subject by dealing with one example—the musical sense in Man. I do not believe that the musical sense had its beginnings in Man, or that it has materially increased since the days of primitive Man, but in conjunction with the higher psychical life of civilized peoples its expressions and applications have risen to a higher level. It is, so to speak, an instrument which has been transmitted to us from our animal ancestors, and on which we have learnt to play better the more our mind has developed; it is an unintended 'accessory effect' of the extremely fine and highly developed organs of hearing with their nerve-centres which our animal ancestors acquired in the struggle for existence, and which played a much more important rôle in the preservation of life in their case than it does in ours. The musical sense may be compared to the hand, which was developed even among the apes, but which civilized Man in modern times no longer uses merely to perform its original function, grasping, but also for many other purposes, such as writing and playing the piano. And just as the hand did not originate through the necessities of the piano, neither did the extremely delicate sense of hearing of the higher animals develop for the sake of music, but rather that they might recognize their enemies, friends, and prey, in darkness and mist, in the forest, on the heath, and at great distances.
The case is probably the same with the rest of the special psychical endowments or talents. I do not of course maintain that they, like the musical sense, did not at some time play a rôle in the struggle for existence and survival, and therefore could not increase, but the increase was certainly not continuous, but much interrupted, so that it would extend only to small groups of descendants, and therefore could only contribute very slowly to the elevation of the psychic capacities of a whole people. But in certain individuals and families such augmentations would certainly take place through germinal selection, and it seems to me probable that these would never be wholly lost again, even if they appeared to be so, but would be handed on, in id-minorities, through the chain of generations, and would slightly raise the average of the talent in question, and might even, under favourable circumstances, combine in the development of a genius. We know how strongly hereditary such specific talents are; let us suppose that the determinants of, say, the musical sense have, by the intra-germinal chances of nutrition, been started on a path of ascending variation; they will continue in this path until a halt is called from some quarter or other. This can only happen if, in the reducing division, or in amphimixis, the highly developed musical determinants are wholly or partly eliminated, or are reduced to a minority. As long as this does not happen the ascending variation will go on, and then we may have the birth of a Mozart or of a Beethoven. Personal selection will not interfere either in a positive or a negative sense, since high development of the musical sense has no effect either in advancing or retarding the struggle for existence; the increase will therefore go on until the large majority of highly developed musical determinants, which we must assume in the case of a musical genius, is reduced, or even transformed into a minority, through unfavourable reducing divisions of the germ-cells, and by association with the germ-cells of less musical mates.
The fact that highly developed specific talents have never been known to be inherited through more than seven generations is quite in keeping with this view. But even this persistence has been observed only in the case of musical talent, and the long continuance of the inherited talent may well be due, as Francis Galton suggests in his famous statistical investigations into the phenomena of inheritance, to the fact that musical men do not readily choose wives who are absolutely lacking in this talent. It would be easy to rear an exceedingly highly gifted musical group of families within the German nation, if we could secure that only the highly-gifted musically should unite in marriage—that is, if personal selection could play its part. In another more general domain of mental endowment a case of this kind has been recorded, for Galton tells us of three highly gifted English families which intermarried for ten generations, and in that time scarcely produced a descendant who did not deserve to be called a distinguished man in some direction or other.
Of course, such continued persistence, through a long series of generations, of a high general mental level is more possible than the transmission and increase of a specific talent, for in the former case it is a question of a mixture of different high mental endowments, of which not all need be developed in every individual, and yet the individual need not fall to mediocrity if he possesses a combination of other qualities. But in musical talent, on the other hand, the falling from the height once attained takes place as soon as this one character is no longer represented in a sufficiently strong majority of determinants. Of course it would be a mistake to believe that the talent of a Sebastian Bach or a Beethoven depended solely on the highly developed musical sense; in them, as in all great artists, many highly developed mental qualities must have combined with the musical sense; a simpleton could never have written the Mass in B minor or the Passion of St. Matthew even if he had possessed the musical genius of Sebastian Bach. In this fact lies a further reason why genius is seldom found at the same pitch in two successive generations; the combination of mental characters always varies from father to son, and slight displacements may give rise to very great differences in relation to the manifestations of the specific talent. Under certain circumstances, the weak development of a single trait of character, as, for instance, power of action, or the excessive development of another, such as indecision or desultoriness, may so nullify the existing favourable combinations of mental characters, such as, let us say, musical sense, inventive talent, depth of feeling, &c., that they bear no fruit worth mentioning. And since as we have already seen, the different mental qualities of the parents are to a certain extent separately transmitted, that is, since they may appear in the children in the most diverse combinations, we should rather be surprised that pronounced talent in a specific direction can persist in a family for two and a half centuries than that it should do so very rarely. For reducing division is always combining the existing mental qualities anew, and amphimixis is adding fresh ones to them.
Thus germinal selection, that is, the free, spontaneous, but definitely directed variation of individual groups of determinants, is at the root of those striking individual peculiarities which we call specific talents; but it can attain to the highest level only rarely and in isolated cases, because these talents are not favoured by personal selection, and therefore the excessively highly developed determinants upon which they depend may be dispersed in the course of generations; they may sink to smaller majorities, or even to minorities, in which case they will no longer manifest themselves in visible mental qualities.
We deduced the process of germinal selection on the basis of the assumption that the nutrition of all the parts and particles of the body, therefore also of the determinants and biophors of the germ-plasm, is subject to fluctuations. We regarded the resulting variations of these last and smallest units of the germ-plasm as the ultimate source of all hereditary variation, and therefore the basis of all the transformations which the organic world has undergone in the course of ages and is undergoing still.
We have still to inquire whether we can give any more precise account of the nature of these units of the germ-plasm. If I mistake not, we may say at least so much, that all variations are, in ultimate instance, quantitative, and that they depend on the increase or decrease of the vital particles, or their constituents, the molecules. For this reason I have hitherto always spoken of only two directions of variation—a plus or a minus direction from the average. What appears to us a qualitative variation is, in reality, nothing more than a greater or a less, a different mingling of the constituents which make up a higher unit, an unequal increase or decrease of these constituents, the lower units. We speak of the simple growth of a cell when its mass increases without any alteration in its composition, that is, when the proportion of the component parts and chemical combinations remains unchanged; but the cell changes its constitution when this proportion is disturbed, when, for instance, the red pigment-granules which were formerly present but scarcely visible increase so that the cell looks red. If there had previously been no red granules present, they might have arisen through the breaking up of certain other particles—of protoplasm, for instance, in the course of metabolism, so that, among other substances, red granules of uric acid or some other red stuff were produced. In this case also the qualitative change would depend on an increase or decrease of certain simpler molecules and atoms constituting the protoplasm-molecule. Thus, in ultimate instance, all variations depend upon quantitative changes of the constituents of which the varying part is composed.
It might be objected to this argument that chemistry has made us acquainted with isomeric combinations whose qualitative differences do not depend upon a different number of the molecules composing them, but upon their different arrangement; it might be supposed that something similar would occur also in morphological relations. And, in point of fact, this seems to be the case. We may, for instance, imagine one hundred hairs as being at one time equally distributed on the back of a beetle, and at another standing close together and forming a kind of brush, but although this brush would be a new character of the beetle, yet its development would depend upon quantitative differences, namely, on the fact that the same skin-area, which in the first case bore perhaps only one hair, had in the second case a hundred. The quantity of hair cells has notably increased upon this small area. In the same way the characteristic striping of the zebra depends not on a qualitative change in the skin as a whole, but upon an increased deposit of black pigment in particular cells of the skin, therefore on a quantitative change. In relation to the whole animal it is a qualitative variation, as contrasted, for instance, with the horse, but in respect of the constituent parts which give rise to the qualitative variation it is purely quantitative. The character of the whole edifice is changed when the proportion of the stones of which it consists are altered.
Thus the determinants of the germ may not only become larger or smaller as a whole, but some kinds of the biophors of which they are made up may increase more than others, under definite altered conditions, and in that case the determinants themselves will vary qualitatively, so that, from the changing numerical proportions of the different kinds of biophors, a variation of the characters of the determinants can arise, and consequently also qualitative variations of the organs controlled by the determinants—the determinates. But, since nothing living can be thought of as invariable, the biophors themselves may, on account of nutritive fluctuations, grow unequally, and thereby vary in their qualities. To follow this out in greater detail and attempt to guess at the play of forces within the minutest life-complexes would at present only be giving the rein to imagination, but in principle no objection can be made to the assumption that every element of life down to the very lowest and smallest can, by reason of inequalities in its nutrition, be not only started on an ascending or descending movement of uniform growth, but can also be caused to vary qualitatively, that is, in its characters, because its component parts change their proportions.