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Page:Popular Science Monthly Volume 57.djvu/411

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401
CAUSES OF DEGENERATION IN BLIND FISHES.

in the shape of a continuous evolutionary process determined by internal causes, in the ease 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 I)y 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