428 PRIM. \RY FA CTORS OF ORGANIC E VOL UTION. 



larger number of animals trained. It is not probable 

 that mere exercise of training could materially further 

 increase this speed, for the next ten years lowered the 

 record only two and a half seconds, and twenty-one 

 years more passed before the first 2:30 record in har- 

 ness was made. 







"By 1848, the record was lowered to 2:29^, and 

 we have now a 2:30 class, with two or three horses 

 technically in it, and perhaps half a dozen that had 

 actually trotted at that speed. Now we began to have 

 distinctively trotting blood, and heredity began to tell. 



"The next decade lowered the record five seconds; 

 and the next (ending in 1868), lowered it seven and a 

 fourth seconds more ; there were several horses in the 

 2:20 class, and nearly one hundred and fifty in the 

 2:30 list. 



( ' The next decade lowered the record four seconds ; 

 and the next (ending in 1888), four and a half seconds, 

 and the number of 2:30 horses had increased to 3,255 

 animals. At the close of last year, the record had 

 been further lowered half a second, to 2:08^" ; there 

 were 5,908 in the 2:30 list, 507 in the 2:20 list, and 

 seven in the 2:10 list. This is the history for seventy- 

 three years of 'records.' 



" Parallel with the evolution of this breed has been 

 the development of a breed of pacers. The fast ani- 

 mals are not so numerous, but the speed is greater, 

 and the gait, as a fast gait, is more distinctly artificial. 

 The instincts involved will be discussed in a later pa- 

 per ; here I will notice only the development of speed, 

 because that is the direct and obvious result of func- 

 tional development, and because we have mathematical 

 data as to the rate and amount of actual evolution. 



"That the gain in speed has been cumulative, and 



