Chap. VIII. HYBRIDS AND MONGEELS. 273 



ous ; but some few cases both of hybrids and mongrels 

 long retaining uniformity of character could be given. 

 The variability, however, in the successive generations 

 of mongrels is, perhaps, greater than in hybrids. 



This greater variability of mongrels than of hybrids 

 does not seem to me at all surprising. For the parents 

 of mongrels are varieties, and mostly domestic varieties 

 (very few experiments having been tried on natural 

 varieties), and this implies in most cases that there has 

 been recent variability ; and therefore we might expect 

 that such variability would often continue and be super- 

 added to that arising from the mere act of crossing. 

 The slight degree of variability in hybrids from the first 

 cross or in the first generation, in contrast with their 

 extreme variability in the succeeding generations, is a 

 curious fact and deserves attention. For it bears on 

 and corroborates the view which I have taken on the 

 cause of ordinary variability ; namely, that it is due 

 to the reproductive system being eminently sensitive 

 to any change in the conditions of life, being thus 

 often rendered either impotent or at least incapable 

 of its proper function of producing offspring identical 

 with the parent-form. Now hybrids in the first gene- 

 ration are descended from species (excluding those 

 long cultivated) which have not had their repro- 

 ductive systems in any way affected, and they are 

 not variable ; but hybrids themselves have their repro- 

 ductive systems seriously affected, and their descend- 

 ants are highly variable. 



But to return to our comparison of mongrels and 

 hybrids : Gartner states that mongrels are more liable 

 than hybrids to revert to either parent-form ; but 

 this, if it be true, is certainly only a difference in 

 degree. Gartner further insists that when any two 

 species, although most closely allied to each other, are 



n 3 



