Chap. VIII. 
HYBRIDS AND MONGRELS. 
273 
than those from very distinct species ; and this shows 
that the difference in the degree of variability gra¬ 
duates away. When mongrels and the more fertile 
hybrids are propagated for several generations an ex¬ 
treme amount of variability in their offspring is noto¬ 
rious ; 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 s]3ecies (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 
N 3 
