20 OKGANIC EVOLUTION — PHYSICAL 



began, the rate of speed evolution (which depends on 

 structural evolution) was comparatively rapid, but that 

 this rate has been gradually slowing, so that now the 

 raccdiorses of one decade do not greatly surpass the 

 race-horses of the previous decade. To some extent 

 this, of course, may be due to the fact that to obtain 

 any increment of speed a more than corresponding 

 increment of force must be put forth, as is exemplified 

 by the fact that an oarsman, to increase his speed from 

 two to four miles an hour, must use more than twice 

 the amount of force, and to increase his speed to six 

 miles an hour, must use a still more disproportionate 

 amount of force. But the race-horse surpasses the 

 ordinary horse not so much because it is more powerful, 

 but because it is better shaped for speed, just as the 

 racing boat surpasses in speed the ordinary rowing boat 

 for the same reason. We can hardly conclude that the 

 evolution of the race-horse is now slow because he has 

 nearly reached the perfection of shape for speed, for 

 another of the equidre, the Avild ass, a smaller animal, 

 is said to be swifter. The decreasino' rate of evolution, 

 therefore, must be set down to another cause. ■ 



If we mate two ordinary horses there is a fair pros- 

 pect that some at least of the offspring will be as fine, 

 or even finer, animals than either the sire or the dam. 

 But if we mate a Derby winner with a good mare — a 

 better mare than his dam — we shall find that the 

 majority of liis progeny are inferior to himself, and that 

 only very exceptionally does he procreate a son or a 

 daughter that can match him for speed. Thus, I 

 venture to say that very few, if any, of the sons or 

 daughters of Ormonde will be his equals. Bapid evolu- 

 tion, therefore, rapidly becomes more slow. Why ? 

 Evidently because there is a tendency for the offspring 

 to omit more or less of the latest evolution of the race 

 and revert to the ancestry, sometimes the remote 



