142 GENETICS AND EUGENICS 



Cats. Domestic cats are descended from a wild species 

 {Felis 7naniculaia) still found in northern Africa. The domes- 

 tication was accomplished in ancient Egypt and the domestic 

 cat was introduced into Europe in the middle ages, since 

 Roman times. The wild species is similar in size and color to 

 the common tabby or tiger cat. This has a coat consisting 

 of agouti-like hairs, which contain both black and j^ellow 

 pigments, but the body is marked with stripes in which black 

 pigment predominates, and it is these black stripes that pro- 

 duce the tiger pattern, which is a dominant unit-character. 

 Different forms of the tiger pattern, distinguished as lined, 

 striped, blotched, etc., are probably multiple allelomorphs. 

 In the self-black variety the tiger pattern and agouti mark- 

 ing of the hairs have been covered up by a greatly increased 

 amount of black. The black variety probably originated as 

 a sport and it behaves as a recessive to tabby. An all yellow 

 variety represents another unit-character variation imper- 

 fectly' dominant over black. Homozygous individuals are 

 all yellow but heterozygous females usually show both yel- 

 low and black (tortoise shell) though occasionally they may 

 be all yellow. The inheritance of yellow is sex-linked and 

 of the Drosophila type. (See Chapter XVIIl.) Yellow cats 

 usually, if not always, show the tiger pattern, which leads 

 to the question whether this pattern is ever lost even in the 

 black variety. It may be only covered up with black pig- 

 ment. Darwin notes the fact that black kittens often show 

 the tiger pattern which is not visible in them later in life. 

 All-white varieties of cats exist having colored eyes (either 

 "yellow" or blue). The relation of this variation to colored 

 forms, as regards dominance, is uncertain, but it probably 

 represents an extreme form of white spotting. Blue (or 

 Maltese) is a dilute form of black, recessive to the latter. 

 The dilution factor probably affects the appearance of tabby 

 and yellow also, but definite information on the point is not 

 available. White spotting is a character the behavior of 

 which as regards dominance is unknown. Yellow spotting 

 occurs only as a heterozygous character in the cross between 



