of the Cessation of Use, but only by supposing that the accumulation of inborn variations has resulted in an overgrowth of protective skin.
This latter, however, is a case of evolution, not of retrogression, and is therefore not due to "what has been called in questionable logic," reversed selection—"the selection which effects not increase of an organ but decrease of it" (p. 13).
Reversed Selection is supposed by some biologists to have operated in another way as a cause of retrogression, viz. by effecting economy of nutrition. They hold that when in any species an organ becomes useless, those individuals that vary in such a manner that in them supplies of nutrition are diverted from the useless organ to useful organs are at an advantage over those individuals which do not so vary, and that this advantage, due to economy of nutrition, is great enough to be an important factor in survival, and that to it therefore is due in whole or part the retrogression of a useless organ.
In championing the opinion that retrogression is due to disuse, Mr. Spencer directs his whole powers of attack against this last theory, quite ignoring the other theories I have discussed, which attribute retrogression (1) to Cessation of Selection as regards useless organs, or (2) to Reversed Selection operating against worse than useless organs, or (3) to the combined action of both Cessation of Selection and Reversed Selection. So far as his arguments go, I think it must be admitted that they are conclusive.
He says, "Suppose that in a new habitat the kangaroo had no enemies; and suppose that, consequently, quickness of hearing not being called for, large ears gave no greater advantage than small ones. Would an individual with smaller ears survive and propagate better than other individuals in consequence
