Lnfluence of Selection 209 
like the old form, but, if interbred, some at least of their descend- 
ants will give the new race. Occasionally the new type bred 
back to the parent type may give a hybrid intermediate between 
the two parents, and this hybrid may become the parent of a new 
race that does not revert to either parent type. These different 
cases will later be considered more fully, For the present it will 
suffice to call attention to the fact that it is generally possible 
in one of these different ways to produce a new race by selection 
and isolation, and it appears probable that sudden variations 
of this kind have furnished the breeder with his most valuable 
material. 
A point of great importance is that the new type may at first 
not differ very much from the original stock; and hence may 
often appear to be only a fluctuation. If, however, the new type 
reappears in the same strength in its offspring, it shows istelf to 
be a mutation and not a fluctuation. Until within quite recent 
years this distinction has not been fully appreciated, and all 
small differences were assumed to be fluctuations. 
The origin of most of our domesticated forms is unknown; 
their history goes back to a remote time. Nevertheless within 
comparatively recent years a number of new types — sports or 
mutations — have arisen and their history is a matter of record. 
A relatively large number of such instances are known to bota- 
nists, and de Vries has recently given a careful analysis of such 
cases that appear to be authentic. Fewer cases are known 
to zodlogists; the more important of these may be briefly 
given. 
The most remarkable instance is that of the ancon ram. 
There appeared in 1791 in a flock of ordinary sheep a ram with 
short legs and a long body. This ram, bred to a ewe of the com- 
mon type, produced descendants having the same characteristics 
as the ancon father. In this way the new race originated which 
breeds true to the new type. The turnspit dog has short and 
crooked legs, recalling the condition of the ancon sheep. Darwin 
states that this kind of monstrosity is not uncommon in various 
animals, and cites the case of jaguars in Paraguay, and of a 
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