II UNIT CHARACTERS 99 



The limitation of unit characters is well brought out in respect 

 ) to color. Butterflies have black, white, red, green (with both its 

 constituents, yellow and blue), and almost all conceivable shades 

 I and markings. Birds have the same, but with few cases of the 

 ! green. Cattle have black, white, red, and a kind of yellow 

 I and blue, but no green. These colors combine, too, both in 

 I spots and roans. Pigs have black, white, and red, in which 

 the combination is frequently spotted (piebald) but never roan. 

 Horses have black, white, and a kind of red, mixed in both 

 spots and roans, but no blue or green ; that is to say, color 

 characters are limited. 



All this means that species are made up of certain definite 

 characters, and these characters run through and among the 

 individuals like colored threads in the warp and woof of cloth, 

 throwing up here one pattern and there another, according to 

 the relative intensity and frequency of the various units. 



What is true of colors and color patterns is true of other 

 characters of the race, and the term " unit character " is a good 

 one to designate these half-independent and half-dependent 

 assortments of physical features that go to make up the various 

 species in nature. It is upon these unit characters separately, 

 and not upon their composite effect, that the attention should 

 now be fixed. 



Every individual possesses all the characters of the race. 

 After being convinced that no two individuals are alike, it is 

 easy to assume that they differ in the particular unit characters 

 they possess. This is a mistake. Every individual possesses all 

 the characters of the race to which he belongs, whether they 

 are evident or not, whether they are developed or undeveloped. 

 Individual differences in most respects are quantitative rather 

 than qualitative, that is, are due to relative development or non- 

 development of characters that belong to the race rather than to 

 actual difference in unit characters. 



Some races are so rich in unit characters that not all can 

 develop in any single individual, as, for example, color in cattle. 



