DIFFICULTIES. 21$ 



tion of these minute, indefinite, irregular, hap- 

 hazard variations has given rise, little by little, 

 to the origin and development of species. The 

 question which naturalists have been trying to settle 

 is, whether selection from variations of this charac- 

 ter are sufficient to produce the. result ascribed to it. 

 The answer which has been generally given is that 

 natural selection of chance variations is not alone 

 sufficient to account for the origin of species. 



Difficulties from the Slowness of the Modification. 



If species must be produced by the selection of 

 such minute variations, change must have taken 

 place very slowly, and the production of a new 

 species will require a great amount of time. Now, 

 making all allowance for error, it seems to be almost 

 certain that the time since the appearance of life in 

 the world has not been great enough to account for 

 the development of the present species by any such 

 process. The time since the Egyptian monuments 

 were made, which represents 4,000-5,00x3 years, has 

 not been long enough to produce any appreciable 

 amount of change in domestic species. Even the 

 much longer time since the glacial period has had 

 very little effect, many species being precisely simi- 

 lar to those of that time. Darwin estimated that 

 300,000,000 years at least would be required to pro- 

 duce the present world of species, while physicists 

 will not admit the possibility of there being more 

 than 100,000,000 years since the world was inhabited, 

 and of late years geologists have been shortening the 

 length of their geological epochs. Whatever be the 



