THE CASE AGAINST DARWINISM Objections to the Theory.-Much has been made by the critics of Darwinism of the alleged uselessness of many char acters. Since variation is not in itself adaptive, they may be useful, harmless or harmful, and so long as they remain harmless, useless variations may remain, since they have no effect on the death-rate ; but so soon as they increase to a harmful extent, they tend to be eliminated. Only favourable variations can be selected and apparent exceptions to this rule may be due to corre lation, which plays an important part in evolution. A factor of inheritance may affect several characters and even the whole organism, so that the alteration of one character by selection may lead to correlated changes in other parts.
Many characters have, however, been asserted to be useless which have subsequently been found to be not only useful, but essential. As our knowledge advances, the functions fulfilled by various organs and parts are daily being discovered. Conspicuous examples are the glands of internal secretion, such as the pituitary gland, formerly supposed to be a useless vestigial structure, but now known to be of the greatest importance. No character can be accepted as useless until its presence or absence has been proved to exert no influence on the death-rate.
It has sometimes been urged by detractors of Darwin's theory, that organisms are pre-adapted and that natural selection does no more than allow what has already been developed to persist. In a certain limited sense this is, of course, true. Selection can only take place between existing forms and variations; and many instances may be given in which organisms have been able to spread into new regions, where others have failed, because they happened to be of suitable structure. Selection cannot be prophetic and such cases are due to chance. But they do not diminish the importance of natural selection in building up organisms fitted to live under special conditions, or organs adapted to fulfil special functions, which is what we really mean by adaptation.
Lastly, it is sometimes objected that if selection cannot be prophetic, if evolution is not due to some purposeful force, it is difficult, if not impossible, to account for the development of such complex organs, since the initial stages would be useless. In this connection it should be remembered that organs are rarely, if ever, known to "begin." Entirely new functions are not sud- , denly developed. A careful study of what we know of their evolution shows that they are evolved by the gradual transforma tion of addition to or subtraction from something already present. The wing of a bird has had no sudden beginning, but has been gradually transformed from the fore-limb of a reptile. An inter mediate stage is seen in the extinct Archaeopteryx (q.v.). The sharp sting of a bee is the transformed ovipositor commonly found in insects. Even such a highly specialized organ as the eye of man may be traced back to the property of response to light distributed over the surface of the body in the lowest animals. No doubt, owing to imperfect knowledge, there are many cases in which the intermediate stages are unknown and difficult to imagine; but it should not be concluded that they have not existed.