142 REVERSION AND ALLIED PHENOMENA 



Conclusion. — In his Locksley Hall Sixty Years After Tennyson 

 spoke of — 



Evolution ever climbing after some ideal good, 



And Reversion ever dragging Evolution in the mud; 



but this is making a bogey of reversion. Many of the phenomena 

 commonly labelled as " reversions " are wrongly labelled, and 

 true Reversion does not seem to be of frequent occurrence. 

 Moreover, when it does occur, it may mean, not a deterioration, 

 but a return to a position of greater organic stability. What 

 acts as a drag or brake — often advantageously — on progressive 

 variation is not so much reversion as filial regression. 



But the great step of progress that has been made of recent 

 years is due to the Mendelian experimenters who have shown 

 that many of the reversions which follow crossing are due to the 

 re-combination of complementary factors which had become 

 separated in the course of domestication and cultivation. 



Wherever this can be shown there is, of course, no warrant for 

 the hypothesis that reversion is due to the sudden activation of 

 a long latent ancestral character. But this hypothesis may be 

 in the meantime retained for any cases that appear to demand it, 



