NATURAL SELECTION 



in explaining the evolution of higher from 

 lower forms of life, appeals only to agencies 

 which are still visibly in action. Whether spe- 

 cies, in a state of nature, are changing or not at 

 the present time, cannot be determined by di- 

 rect observation, any more than the motion of 

 the hour-hand of a clock could be detected by 

 gazing at it for one second.^ The entire period 

 which has elapsed since men began to observe 

 nature systematically is but an infinitesimal por- 

 tion of the period requisite for any fundamen- 

 tal alteration in the characteristics of a spe- 

 cies. But there are innumerable cases in which 

 species are made to change rapidly through the 

 deliberate intervention of man. In the course 

 of a few thousand years, a great number of 

 varieties of plants and animals have been pro- 

 duced under domestication, many of which 

 ^ ** If we imagine mankind to be contemplated by some 

 creature as short-lived as an ephemeron, but possessing intelli- 

 gence like our own — if we imagine such a being studying men 

 and women, during his few hours of life, and speculating as 

 to the mode in which they came into existence ; it is manifest 

 that, reasoning in the usual way, he would suppose each man 

 and woman to have been separately created. No appreciable 

 changes of structure occurring during the few hours over which 

 his observations extended, this being would probably infer that 

 no changes of structure were taking place, or had taken place ; 

 and that from the outset, each man and woman had possessed 

 all the characters then visible — had been originally formed 

 with them. This would naturally be the first impression,'* 

 Spencer, Principles of Biology, vol. i. p. 338. 

 II 



