Seite - 519 - in The Origin of Species

RECAPITULATION AND CONCLUSION 519 of embryological and homologous structures, but we are too blind to understand her meaning. I have now recapitulated the facts and considerations which have thoroughly convinced me that species have been modified, during a long course of descent. This has been effected chiefly through the natural selection of numerous successive, slight, favourable variations ; aided in an im- portant manner by the inherited effects of the use and dis- use of parts; and in an unimportant manner, that is in rela- tion to adaptive structures, whether past or present, by the direct action of external conditions, and by variations which seem to us in our ignorance to arise spontaneously. It ap- pears that I formerly underrated the frequency and value of these latter forms of variation, as leading to permanent modi- fications of structure independently of natural selection. But as my conclusions have lately been much misrepre- sented, and it has been stated that I attribute the modifica- tion of species exclusively to natural selection, I may be per- mitted to remark that in the first edition of this work, and subsequently, I placed in a most conspicuous position— namely, at the close of the Introduction the following words : "I am convinced that natural selection has been the main but not the exclusive means of modification." This has been of no avail. Great is the power of steady misrepresenta- tion; but the history of science shows that fortunately this power does not long endure. It can hardly be supposed that a false theory would ex- plain, in so satisfactory a manner as does the theory of nat- ural selection, the several large classes of facts above speci- fied. It has recently been objected that this is an unsafe method of arguing; but it is a method used in judging of the common events of life, and has often been used by the greatest natural philosophers. The undulatory theory of light has thus been arrived at; and the belief in the revolu- tion of the earth on its own axis was until lately supported by hardly any direct evidence. It is no valid objection that science as yet throws no light on the far higher problem of the essence or origin of life. Who can explain what is the essence of the attraction of gravity? No one now objects to following out the results consequent on this unknown