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 
and markings. Birds have the same, but with few cases of the 
green. Cattle have black, white, red, and a kind of yellow 
and blue, but no green. ‘These colors combine, too, both in 
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. 
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