EVOLUTION BY LOSS 



The simplest variation from this ancestral 

 type of coloration is albinism, a wholly unpig" 

 mented condition in which the eyes are pink. 

 This is due to the loss of the capacity to form 

 pigment. Albinism is recessive in crosses. We 

 explain it by assuming that something neces- 

 sary for color production is wanting in the 

 albino, and call that something the color-factor 

 C, without necessarily making any assumption 

 as to its nature. Another common variation 

 is the loss of the pattern-factor of the indi- 

 vidual hair, the agouti or A factor. An ac- 

 count of the discovery of this factor was given 

 in the last chapter. In consequence of the loss 

 of this factor the pigments become mingled 

 together without order, and the result is a 

 uniform black, the denser pigment hiding the 

 others. 



A third variation is the loss of the capacity 

 to form black pigment (factor B), only brown 

 and yellow pigments being left. Thus arise 

 brown and cinnamon varieties. Through these 

 three independent loss-variations there arise 

 eight different color-varieties as follows: 



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