120 Selection Does Not Lead to Origin of Species. 



probably owes its origin partly to the fact that the num- 

 ber of individuals is vastly increased during that period 

 and partly to the frequent discovery of subspecies which 

 previously had been overlooked. 



4. Regression. Selection is succeeded by regression, 

 which is great in proportion to the stringency of the 

 selection which preceded it. However long the selection 

 is maintained it is always follow^ed by regression. It 

 appears that much more than half of wdiat was gained 

 is lost after cessation of selection. The mean of the 

 character so far as we know^ cannot be altered ; regression 

 always aims at the bull's eye of the specific character. 

 I shall return to this point in the next section. 



We may lay it down as a general rule that a doubling 

 or a halving of the original mean is about the most that 

 can be attained by selection. And usually one has to put 

 up with much more meagre improvement.- The most 

 conspicuous case of variability is the increase in fleshi- 

 ness in fruits and roots, but this exception is only ap- 

 parent.^ 



5. The Instability of Races. The chief difference 

 between improved races and species, even the smallest 

 elementary species, is the instability of the former and 

 the stability of the latter. Races that have arisen by 

 selection can only be preserved by continuing that pro- 

 cess; it costs as much trouble to retain them as it did 

 to obtain them. If selection of the race ceases, the char- 

 acters of the race fade away. And the time it takes 

 them to disappear is the same as it took them to appear. 

 In a few generations they come ; in a few also do they go. 



^Compare the figures given in Wallace's Darzvinism, p. 8i. 

 '' The crab apple is more than half the size of most of our eating 



apples 



