Page:Popular Science Monthly Volume 33.djvu/67

Rh dogma, which is really a curious phenomenon in the history of thought. "We may fitly ask," he says, whether it "accounts for" organic evolution. "On critically examining the evidence," he proceeds, "we shall find reason to think that it by no means explains all that has to be explained." And then follows an allusion of curious significance. "Omitting," says Mr. Spencer, "for the present any consideration of a factor which may "be distinguished as primordial—" Here we have the mind of this distinguished philosopher confessing to itself—as it were in a whisper and aside—that Darwin's ultimate conception of some primordial "breathing of the breath of life" is a conception which can only be omitted "for the present." Meanwhile he goes on with a special, and it must be confessed a most modest, suggestion of one other "factor" in addition to natural selection, which he thinks will remove many difficulties that remain unsolved when natural selection is taken by itself. But while great interest attaches to the fact that Mr. Herbert Spencer does not hold natural selection to be the sole factor in organic evolution, it is more than doubtful whether any value attaches to the new factor with which he desires to supplement it. It seems unaccountable indeed that Mr. Herbert Spencer should make so great a fuss about so small a matter as the effect of use and disuse of particular organs as a separate and a newly recognized factor in the development of varieties. That persistent disuse of any organ will occasion atrophy of the parts concerned, is surely one of the best established of physiological facts. That organs thus enfeebled are transmitted by inheritance to offspring in a like condition of functional and structural decline, is a correlated physiological doctrine not generally disputed. The converse case—of increased strength and development arising out of the habitual and healthy use of special organs, and of the transmission of these to offspring—is a case illustrated by many examples in the breeding of domestic animals. I do not know to what else we can attribute the long, slender legs and bodies of greyhounds so manifestly adapted to speed of foot, or the delicate powers of smell in pointers and setters, or a dozen cases of modified structure effected by artificial selection.

But the most remarkable feature in the elaborate argument of Mr. Spencer on this subject is its complete irrelevancy. Natural selection is an elastic formula under which this new "factor" may be easily comprehended. In truth, the whole argument raised in favor of structural modification arising out of functural [sic] use and disuse, is an argument which implies that Mr. Spencer has not himself entirely shaken off that interpretation of natural selection which he is disputing. He treats it as