426 PRIMARY FACTORS OF ORGANIC EVOLUTION. 



all the smaller breeds have originated in districts of 

 scantier forage. This can hardly be due to accident, 

 for it is as true of local varieties of wild animals under 

 natural selection as of domestic animals under artifi- 

 cial selection." 



b. Inheritance of Characters Due to the Exercise of 



Function. 



This class of cases has an especial bearing on the 

 doctrine of kinetogenesis. We have a very conspicu- 

 ous example of such inheritance in the case of the 

 evolution of the trotting horse, which is described by 

 Professor Brewer as follows : 



"We have a copious literature relating to the de- 

 velopment of this breed, and the * records ' of speed 

 provide the data for a mathematical history of the rate 

 of progress, and also the measure of amount of cumu- 

 lative variation that has occurred up to this time. 

 These data give to this breed a special interest for 

 scientific study. 



"The facts briefly stated are as follows : Trotters 

 had their uses for ages, but fast trotters were not 

 wanted until the improvement in roads and in wheeled 

 vehicles during the last quarter of the last century 

 caused an increasing demand for faster roadsters for 

 light draft. Trotting is the gait of traction, as run- 

 ning is for riding, and trotting as a sport sprang up in 

 nearly all the countries of Europe as well as in Amer- 

 ica so soon as faster trotters were needed for the road. 

 Then trotting-horses began to be bred, and long be- 

 fore the close of the century there were trotting-stal- 

 lions of considerable fame. There were also recorded 

 statements as to the speed attained. 



"Lawrence, a lover of trotters, in his Treatise on 



