NATURAL SELECTION 67 



ists generally, that, given a sufficient length of time 

 and slowly varying conditions, such as exist upon the 

 earth, there is no practical limit to the amount of 

 variation of organic forms that may slowly take place, 

 and that natural selection is, for the most part, suffi- 

 cient to account for the preservation of favorable 

 variations, thus accumulating .them in certain direc- 

 tions. It is not, however, commonly held that 

 natural selection alone will account for the evolution 

 of all organic forms. 



Darwin says that "Natural selection acts solely 

 through the preservation of variations in some way 

 advantageous, which consequently endure." Again 

 he says, " It may metaphorically be said that natural 

 selection is daily and hourly scrutinizing, throughout 

 the world, the slightest variations; rejecting those 

 that are bad, preserving and adding up all that are 

 good; silently and insensibly working, whenever and 

 wherever opportunity offers, at the improvement of 

 each organic being in relation to its organic and in- 

 organic conditions of life. We see nothing of these 

 slow changes in process, until the hand of time has 

 marked the lapse of ages, and then so imperfect is 

 our view into long-past geological ages, that we see 

 only that the forms of life are now different from 

 what they formerly were." 



Again he says, " I believe that animals are de- 

 scended from at most only four or five progenitors, 

 and plants from an equal or lesser number. 



" Analogy would lead me one step further, namely, 

 to the belief that all animals and plants are descended 

 from some one prototype. But analogy may be a 

 deceitful guide." 



In these quotations are clearly set forth the general 

 claims of the theory of natural selection. 



It is true that in the organic world there exist the 



