UNIT CHARACTERS 103 



Fig. 16, 1 or of an entire strain, as in cattle and pigs, and 

 sometimes in a modified color, due to the absence of the 

 definite pigment. 



New characters. It is much easier to understand the extinc- 

 tion of characters and species than it is to account for the 

 appearance of new ones ; indeed, there is some reason to be- 

 lieve that both the fauna and the flora of the world are getting 

 simpler, that is, so far as numbers of species are concerned, by 

 which is meant that, in all likelihood, species are becoming ex- 

 tinct faster than new ones are appearing. 



However, new characters are appearing and, as we shall see 

 later, new strains and races, equivalent for present purposes to 

 new species, are constantly developing. These arise sometimes 

 through the loss of a character, but often by some new combi- 

 nations of old characters, resulting essentially in new races. 

 Good examples of this are found in the large number of new 

 strains of garden flowers, fruits, and vegetables, each with some 

 distinguishing trait that is especially valuable. 



Characters and unit characters. A distinction must be here 

 observed for the sake of accuracy. The term " character " is 

 used in a very general sense to cover any quality or faculty of 

 animal or plant to which we especially desire to allude. 



For example, we speak of the quality of milk production, 

 which, as a valuable commercial consideration in cattle, may be 

 roughly spoken of as a character. Upon reflection, however, it 

 will be seen that it is not a unit character, for the faculty arises 

 not from a single physiological function but from several ; that 

 is to say, there are a variety of facts that would influence milk 

 production, namely, the size of the udder, the glandular activity 

 of the organ, the capacity to eat and digest large amounts of 

 food, and perhaps a number of others unknown to us. 



1 Such a deer would of course have little chance of being spared either 

 by the hunter or by natural enemies ; hence no strain of albino deer can de- 

 velop. The same is true as to albinism in bears, except in arctic regions where 

 conditions are reversed. 



