Influence 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 cither 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 zoologists; 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, recalhng 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 



