Darwin’s doctrine, however, on the origin and significance of rudimentary organs has been damaged by genetic analysis in a yet more serious fashion. In fact, with the discovery that anomalous _suppression_ and anomalous _duplication_ of organs may result from _factorial mutation_, this Darwinian conception received what is tantamount to its deathblow. Darwin, it will be remembered, was convinced that the regression of organs was brought about by “increased disuse controlled by natural selection.” (Cf. “Origin of Species,” 6th ed., ch. V.) Such phenomena, he thought, as the suppression of wings in the Apteryx and the reduction of wings in running birds, arose from their “inhabiting ocean islands,” where they “have not been exposed to the attacks of beasts, and consequently lost the power of using their wings for flight.” (“Descent of Man,” 6th ed., ch. I, p. 32.) In some cases, he believed that disuse and natural selection had coöperated _ex aequo_ to produce results of this nature, _e.g._ the reduction of the eyes in the mole and in Ctenomys; for this reduction, he claims, has some selection-value, inasmuch as reduction of the eyes, adhesion of the lids, and covering with hair tends to protect the unused and useless eye against inflammation. In other cases, however, he is inclined to discount the idea that suppression of organs is an “effect of long-continued disuse,” and to regard the phenomenon as “wholly, or mainly, due to natural selection,” _e.g._ in the case of the wingless beetles of the island of Madeira. “For during successive generations,” he reasons, “each individual beetle which flew least, either from its wings having been ever so little less developed or from indolent habit, will have had the best chance of surviving from not being blown out to sea; and, on the other hand, those beetles which most readily took to flight would oftenest have been blown to sea, and thus destroyed.” In a third class of instances, however, he assigns the principal rôle to disuse, _e.g._ in the case of the blind animals “which inhabit the caves of Carniola and Kentucky, because,” as he tells us, “it is difficult to imagine that eyes, though useless, could be injurious to animals living in darkness.” Hence he concludes that, as the obliteration of eyes has no selection-value, under the circumstances prevailing in dark caves, “their loss may be attributed to disuse.” (Cf. “Origin of Species,” 6th ed., ch. V, pp. 128-133.)