102 Evolution and Adaptation 
and a species, this source of doubt would not so perpetually 
recur.” 
The point here raised in regard to the systematic value of 
the new forms is the question that first demands our attention. 
We must exclude all those cases in which several original 
species have been blended to make a new form, because the 
results are too complicated to make use of at present. The 
domesticated races of dogs appear to have had such a mul- 
tiple origin, the origin of horses is in doubt; but the domesti- 
cated pigeons, ducks, rabbits, and fowls are supposed, by 
Darwin, to have come each from one original wild species. 
The great variety of the domestic pigeons gives perhaps the 
most striking illustration of changes that have taken place 
under domestication; and Darwin lays great stress on the 
evidence from this source. 
It seems probable in this case, (1) that all the different 
races of pigeons have come from one original species; (2) that 
the structural differences are in some respects as great as those 
recognized by systematists as specifically distinct; (3) that the 
different races breed true to their kind; (4) that the result 
has been reached mainly by selecting and isolating variations 
that have appeared under domestication, and that probably 
some, at least, of these variations were fluctuating ones. 
Does not this grant all that Darwin contends for? In one 
sense, yes; in another, no! The results appear to show that 
by artificial selection of some kind a group of new forms may 
be produced that in many respects resemble a natural family, 
or a genus; but if this is to be interpreted to mean that the 
result is the same as that by which natural groups have 
arisen, then I think that there are good reasons for dissenting 
from such a conclusion. Moreover, we must not grant. too 
readily that the different races of pigeons have arisen by the 
selection of fluctuating variations alone, for this is not estab- 
lished with any great degree of probability by the evidence. 
In regard to the first point we find that one of the most 
