It is even conceivable that in the case of cer tain organs no longer needed because of a change of habits of the species, the individuals retaining the organ in full size and develop ment might be handicapped in the struggle for existence through the necessity of its being necessary to divert some of their food and air to the nutrition of these useless parts, while others born with the parts smaller or less de veloped would have a certain useless expendi ture of nutrition on the unnecessary parts. These latter individuals might be assumed there fore to have a little advantage in the bitter struggle for existence by being able to use more of their food and oxygen for the other more important parts of the body.
This sounds rather far fetched, but it has been seriously proposed by extreme Darwinians, who assume that the struggle for existence is so rigorous that even the most minute advantage can turn the scale for or against any individual or species.
Herbert Spencer tried to reduce this posi tion to an absurdity by taking as an example the tiny rudimentary bones of the whale's limbs. These bones are but a few inches long in a body that may be a hundred feet long, and of correspondingly enormous mass. How much food is saved to the whale, asks Spencer, that finds itself born with leg-bones a few milli meters shorter than those in another whale? Can anyone of sane mind conceive or admit of a life-and-death determining advantage in this minute difference in nutritive necessity? So the situation to-day as regards a suffi cient explanation of the actual evolutionary re sults of disuse and the actual causes of the de generation in species of disused parts, result ing in so-called rudimentary or vestigial organs, is far from satisfactory. We know that disuse
of parts by any individual results in degenera tion of such parts in the particular individual concerned, but how it can result in an inherited and increasing degeneration or loss of the parts throughout the species is not clear.
The proponents of the newest theory offered to explain evolution, the mutations theory, have no more satisfactory explanation of the results of disuse, as these results affect the species, than have those who cling to the older evolution theories. Their theory would simply explain the occasional sudden appearance of an indi vidual, or of several individuals in any species, with any one or several organs in undeveloped or rudimentary condition, and this congenital character could be handed on by inheritance. But original use or disuse would have nothing to do with the sudden appearance of the new condition of the organ, nor would the new condition appear necessarily in an animal or species in which it would be an advantage.
Of all the explanations of the evolutionary results of disuse, the Lamarckian one is the simplest, the most rational and most plausible. But it can have no real standing until it can be proved that acquired characters, or certain cate gories of them, including the changes produced in the individual by disuse, can be handed down to the next generation by inheritance.