292 CEEATION EY LAW. 



amount of change has been effected it becomes slower 

 and slower, till at length its limits are reached and no 

 care in breeding and selection can produce any further 

 advance. The race-horse is chosen as an example. 

 It is admitted that, with any ordinary lot of horses 

 to begin with, careful selection would in a few years 

 make a great improvement, and in a comparatively 

 short time the standard of our best racers might be 

 reached. But that standard has not for many years 

 been materially raised, although unlimited wealth and 

 energy are expended in the attempt. This is held to 

 prove that there are definite limits to variation in any 

 special direction, and that we have no reason to sup- 

 pose that mere time, and the selective process being 

 carried on by natural law, could make any material 

 difference. But the writer does not perceive that this 

 argument fails to meet the real question, which is, not 

 whether indefinite and unlimited change in any or all 

 directions is possible, but whether such differences as 

 do occur in nature could have been produced by the 

 accumulation of variations by selection. In the matter 

 of speed, a limit of a definite kind as regards land 

 animals does exist in nature. All the swiftest animals 

 deer, antelopes, hares, foxes, lions, leopards, horses, 

 zebras, and many others, have reached very nearly the 

 same degree of speed. Although the swiftest of each 

 must have been for ages preserved, and the slowest 

 must have perished, we have no reason to believe 

 there is any advance of speed. The possible limit 

 under existing conditions, and perhaps under possible 



