138 THE THEORY OF MUTATION 



is constructed. The entries in this table show the 

 fastest times recorded for the feat of trotting a measured 

 mile in various years beginning with 1818. The ver- 

 tical scale contains the times, which vary from three 

 minutes down to one minute fifty-six seconds, and the 

 horizontal scale shows the year in which the record was 



2.00 

 2,10 

 2,20 

 2,30 

 2,40 

 2,50 

 3,00 



Year 1020 '30 '4-0 'SO 'GO '70 '80 '90 1300 



FIG. ii. 



The figures to the left of the diagram are to be read as minutes and 



seconds. 



made. Some part of the improvement shown is clearly 

 to be associated with better tracks, improved methods 

 of training, etc., but these will scarcely affect the 

 general character of the improvement due to selec- 

 tion. As may readily be seen from the diagram, the 

 improvement is at first rapid, but afterwards becomes 



