Page:Popular Science Monthly Volume 42.djvu/834

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THE POPULAR SCIENCE MONTHLY.

would profit the organism. The economy in weight to a creature having nearly the same specific gravity as its medium, would be infinitesimal. The economy in nutrition of a rudimentary organ, consisting of passive tissues, would also be but nominal. The only appreciable economy would be in the original building up of the creature's structures; and the hypothesis of Weismann implies that the economy of this thousandth part of its weight, by decrease of the eyes, would so benefit the rest of the creature's organization as to give it an appreciably greater chance of survival, and an appreciably greater multiplication of descendants. Does any one accept this inference?

Of course the qualifications of data above set down can be only approximate; but I think no reasonable changes of them can alter the general result. If, instead of supposing the eyes to have disappeared wholly, we recognize them as being in fact rudimentary, the case is made worse. If, instead of two thousand generations, we assume ten thousand generations, which, considering the probably great age of the caverns, would be a far more reasonable assumption than the other, the case is made still worse. And if we assume larger variations—say decreases of one fourth—to occur only at intervals of many hundreds or thousands of generations, which is not a very reasonable assumption, the implied conclusion would still remain indefensible. For an economy of 1200 part of the creature's weight could not appreciably affect its survival and the increase of its posterity.

Is it not then, as said above, that the use of the expression, "natural selection," has had seriously perverting effects? Must we not infer that there has been produced in the minds of naturalists, the tacit assumption that it can do what artificial selection does—can pick out and select any small advantageous trait; while it can, in fact, pick out no traits, but can only further the development of traits which, in marked ways, increase the general fitness for the conditions of existence? And is it not inferable that, failing to bear in mind the limiting condition, that to become established an advantageous variation must be such as will, other things remaining equal, add to the prosperity of the stirp, many naturalists have been unawares led to espouse an untenable hypothesis?—Contemporary Review.

[To be concluded.]

    a liberal estimate, therefore, to suppose that its original weight in the Proteus was 11000 of that of the body. I may add that any one who glances at the representation of the axolotl, will see that, were the eye to disappear entirely by a single variation, the economy achieved could not have any appreciable physiological effect on the organism.