UNIT-CHARACTERS OF DOGS 139 



A different opinion as to the ancestry of dogs has recently 

 been expressed by G. S. Miller and particularly by G. M. 

 Allen, who has made a careful study of the cranial characters 

 of dogs kept by the aboriginees of the American continent. 

 Allen finds strong evidence that the native dogs of America 

 are not descended from American wolves but came with man 

 in his migration from north-eastern Asia to north-western 

 America. Previous to that migration there existed in Europe 

 and Asia both a large and a small type of dog, and both types 

 were introduced into America when it was peopled from 

 Asia. A third type, the Eskimo dog with heavy coat and 

 tail curled forward over the hip, occurs in the northernmost 

 parts of both Asia and America and doubtless came with the 

 Eskimos in their comparatively recent migration from Asia. 

 What part, if any, species hybridization has played in the 

 genesis of dogs can not at present be stated, but a survey of 

 existing breeds of dogs shows the occurrence among them of 

 several unit-characters and accordingly unit-character varia- 

 tion (mutation) may be regarded as having been an import- 

 ant element in their production. A case which well illus- 

 trates the point is the color variation of Great Danes as 

 worked out by Little and Jones. (See Fig. 104a.) Starting 

 with the self black variety (3, Fig. 104a), we have as its reces- 

 sive allelomorphs either brindle (4) or fawn (5) . A recessive 

 dilution factor, if present in a homozygous condition, gives 

 us dilute black (6), dilute brindle (7) and dilute fawn (8). 

 A dominant factor for white spotting produces the harlequin 

 variety (2). A recessive factor for white spotting produces 

 white feet or breast spot (1). These t^^^es of white spotting 

 remind us respectively of the English and Dutch patterns of 

 white spotting among rabbits. Presumably either pattern 

 might occur in association with dilute black, brindled, dilute 

 brindled, fawn, or dilute fawn coat (4-8, Fig. 104a). AVliat 

 are probably more developed forms of the recessive type of 

 white spotting are represented in Figs. 100-109. In the 

 breeds there shown white spotting has been selected lor, 

 whereas in the Great Dane it is rigidly selected against. A 



