The Origin of Species 305 



genetic or fluctuating variations, and those which 

 may be assumed to be of hereditary value. 



VARIATION 



That all organisms vary is plain from the most 

 casual study. Not only are no two individuals ex- 

 actly alike, but no two organs of an individual are 

 identical. Thus it would be impossible to pick out 

 two leaves or flowers which are the same in all re- 

 spects. The source of these variations, and their 

 value in the evolution of new species, are the ques- 

 tions which are engaging the attention of many 

 biologists at the present time. 



In attempting to determine the causes of these 

 universal variations, we at once meet with an almost 

 unsurmountable obstacle. It is practically impossi- 

 ble to determine to what degree the differences be- 

 tween two plants of the same species, growing under 

 apparently the same conditions, are due to inherent 

 peculiarities, and how much to extrinsic factors 

 which may not be evident. That there are individ- 

 ual idiosyncrasies in plants, as well as in animals, is 

 certain. No two individuals in a lot of seedlings 

 will be exactly alike, and the differences may be very 

 striking; but what causes the apparently greater in- 

 herent robustness, for example, of one and the weak- 

 ness of another, is difficult to analyze. Whatever 

 may have been the cause of the superiority of cer- 

 tain individuals, the superiority is evident, and must 



