392 OUTLINES OF EVOLUTIONARY BIOLOGY 



modifying species, and also, to some extent, that of the direct 

 action of the environment : 



" Disuse, aided sometimes by natural selection, will often have 

 reduced organs when rendered useless under changed habits or 

 conditions of life ; and we can understand on this view the 

 meaning of rudimentary organs. 1 But disuse and selection will 

 generally act on each creature, when it has come to maturity 

 and has to play its full part in the struggle for existence, and 

 will thus have little power on an organ daring early life ; hence 

 the organ will not be reduced or rendered rudimentary at this 

 early age. The calf, for instance, has inherited teeth, which 

 never cut through the gums of the upper jaw, from an early pro- 

 genitor having well-developed teeth ; and we may believe, that 

 the teeth in the mature animal were formerly reduced by disuse, 

 owing to the tongue and palate, or lips, having become 

 excellently fitted through natural selection to browse without their 

 aid ; whereas in the calf, the teeth have been left unaffected, and 

 on the principle of inheritance at corresponding ages have been 

 inherited from a remote period to the present day." 2 



" 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 important manner by the 

 inherited effects of the use and disuse of parts ; and in an 

 unimportant manner, that is in relation to adaptive structures, 

 whether past or present, by the direct action of external condi- 

 tions, and by variations which seem to us in our ignorance to 

 arise spontaneously. It appears that I formerly underrated the 

 frequency and value of these latter forms of variation, as leading 

 to permanent modifications of structure independently of natural 

 selection. But as my conclusions have lately been much mis- 

 represented, and it has been stated that I attribute the modifica- 

 tion of species exclusively to natural selection, I may be permitted 

 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 misrepresentation ; but the history of science 

 shows that fortunately this power does not long endure." 3 



1 Often now called " vestigial organs." 

 a "Origin of Species," Ed. vi. p. 420. 

 8 Ibid., p. 421. 



