[N] The Monist, 1896, pp. 250–274.
“The phenomena observed in the stunting, or degeneration, of parts rendered useless ... show distinctly that ordinary selection, which operates by the removal of entire persons—personal selection, as I prefer to call it—can not be the only cause of degeneration, for in most cases of degeneration it can not be assumed that slight individual vacillations in the size of the organ in question have possessed selective value. On the contrary, we see such retrogressions effected apparently in the shape of a continuous evolutionary process determined by internal causes, in the case of which there can be no question whatever of selection of persons or of a survival of the fittest—that is, of individuals with the smallest rudiments. The gradual diminution continuing for thousands and thousands of years and culminating in its final and absolute effacement” can only be accomplished by germinal selection. Germinal selection as applied to degeneration is the formal explanation of Romanes’ failure of heredity through the struggle of parts for food. “Powerful determinants will absorb nutriment more rapidly than weaker determinants. The latter, accordingly, will grow more slowly and will produce weaker determinants than the former.” If an organ is rendered useless, the size of this organ is no longer an element in personal selection. This alone would result in a slight degeneration. Minus variations are, however, supposed to rest “on the weaker determinants of the germ, such as absorb nutriment less powerfully than the rest. This will enable the stronger determinants to deprive them even of the full quantum of food corresponding to their weakened capacity of assimilation, and their descendants will be weakened still more. Inasmuch, now, as no weeding out of the weaker determinants of the hind leg [or eye] by personal selection takes place on our hypothesis, inevitably the average strength of this determinant must slowly but constantly diminish—that is, the hind leg [or eye] must grow smaller and smaller until it finally disappears altogether.... Panmixia is the indispensable precondition of the whole process; for, owing to the fact that persons with weak determinants are just as capable of life as those with strong, ... solely by this means is a further weakening effected in the following generations.”
This theory presupposes the complex structure of the germ plasm formulated by Weismann and rejected by various persons for various reasons. But granting Weismann the necessary structure of the germ plasm, can germinal selection accomplish what is claimed for it? I think not. Granting that variations occur about a mean, would not all the effects claimed for minus variations be counteracted by positive variations? Eye determinants, which, on account of their strength, secure more than their fair share of food, and thereby produce eyes that are as far above the mean as the others are below, and leave descendent determinants that are still stronger than their ancestry would balance the effect produced by weak-eye determinants. It is evident that a large, really extravagant development of the eye in such a fish as Chologaster would not effect the removal of the individual by personal selection; still less so in Amblyopsis, which not only lives in comparative abundance, but has lived for twenty months in confinement without visible food, and in which the eye is minute. It seems that all the admitted objections to degeneration by panmixia apply with equal force to germinal selection. This, however, would be changed were the effect of disuse admitted to affect the determinants, and this it seems Weismann has unconsciously admitted. So far we have considered germinal selection in the abstract only. All its suppositions are found to be but a house of cards when the actual conditions of degeneration are considered. We find that degeneration is not a horizontal process affecting all the parts of an organ alike, as Weismann presupposes, not even a process in the reverse order of phyletic development, but the more vital, most worked parts degenerate first with disuse and panmixia; the passive structures remain longest. The rate of degeneration is proportional to the past activity of the parts, and the statement that “passively functioning parts—that is, parts which are not alterable during the individual life by function—by the same laws also degenerate when they become useless” finds no basis in fact, and is an example of the inexact utterances abundant in the discussion of degeneration on which it is entirely unsafe to build lofty theoretical structures. As one example of the unequal degeneration we need only call attention to the scleral cartilages and the rest of the eye of Troglichthys rosæ.
All are agreed that natural selection alone is insufficient to explain all, if any, of the processes of degeneration. All either consciously or not admit the principle of panmixia, and all are now agreed that this process alone can not produce extensive degeneration. All are agreed that the important point is degeneration beyond the point reached by panmixia, the establishment of the degenerating process, whatever it may be, in the germ, or, in other words, the breaking of the power of heredity. It is in the explanation of the latter that important differences of opinion exist.
Weismann attempts to explain the degeneration beyond the point which panmixia can reach by a process which not only is insufficient, even if all his premises are granted, to produce the desired result without the help of use transmission, but has as its result a horizontal degeneration which has no existence in fact.
Romanes supposed degeneration, beyond the point which may be reached by panmixia, to be the result of personal selection and the failure of the hereditary force. The former is not applicable to the species in question, and is denied by such an ardent Darwinist as Weismann to be applicable at all in accounting for degeneration. Moreover, the process as explained by Romanes would result in a horizontal degeneration which has no existence in fact. The second assumption, the failure of hereditary force, is not distinguishable, as Morgan has pointed out, from the effect of use transmission.
Figs. 1–6.—Photographs of the upper halves of the heads of specimens of nearly the same length under the same magnification, to show the gradual decrease of the eye. The dotted line leads to the eye in all cases.
Fig. 1.—Zygonectes notatus.
Fig. 2.—Chologaster papilliferus.
Fig. 3.—Chologaster Agassizii.
Fig. 4.—Amblyopsis spelæus.
Fig. 5.—Troglichthys rosæ.
Fig. 6.—Typhlichthys subterraneus.
The struggle of parts in the organism has not affected the eye through the lack of room, since the space formerly occupied by the eye is now filled by fat and not by an actively functioning organ. It is not affected by the struggle for food, for stored food occupies the former eye space. It could only be affected by the more active selection of specific parts of food by some actively functioning organ. It is possible that this has in fact affected the degeneration of the eye. The theory explains degeneration in the individual, and implies that the effect in the individual should be transmitted to the next generation. This second part seems but the explanation of the workings of the Lamarckian factor.