Chap. Y. 
LAWS OF VAEIATIOK. 
161 
distant, but that in each successive generation there has 
been a tendency to reproduce the character in question, 
which at last, under unknown favourable conditions, 
gains an ascendancy. For instance, it is probable that 
in each generation of the barb-pigeon, which produces 
most rarely a blue and black-barred bird, there has 
been a tendency in each generation in the plumage to 
assume this colour. This view is hypothetical, but could 
be supported by some facts; and I can see no more 
abstract improbability in a tendency to produce any cha¬ 
racter being inherited for an endless number of genera¬ 
tions, than in quite useless or rudimentary organs being, 
as we all know them to be, thus inherited. Indeed, we 
may sometimes observe a mere tendency to produce a 
rudiment inherited: for instance, in the common snap¬ 
dragon (Antirrhinum) a rudiment of a fifth stamen so 
often appears, that this plant must have an inherited 
tendency to produce it. 
As all the species of the same genus are supposed, on 
my theory, to have descended from a common parent, 
it might be expected that they would occasionally vary 
in an analogous manner; so that a variety of one species 
would resemble in some of its characters another species; 
this other species being on my view only a well-marked 
and permanent variety. But characters thus gained 
would probably be of an unimportant nature, for the 
presence of all important characters will be governed 
by natural selection, in accordance with the diverse 
habits of the species, and will not be left to the mutual 
action of the conditions of life and of a similar in¬ 
herited constitution. It might further be expected 
that the species of the same genus would occasionally 
exhibit reversions to lost ancestral characters. As, how¬ 
ever, we never know the exact character of the common 
ancestor of a group, we could not distinguish these two 
