November 3, 1905.] 



SCIENCE. 



557 



there is practically a species to each island, 

 except that in some cases the species has 

 not spread from the mountain or island in 

 which we may suppose it to have been orig- 

 inally developed. 



There are a few other song birds in the 

 Hawaiian Islands, not related to the Dre- 

 panid^. These are derived from the islands 

 of Polynesia and have deviated from the 

 original types in a degree corresponding 

 to their isolation. 



In the case of the Drepanidag it seems 

 natural to conclude that natural selection 

 is responsible for "the physiological adap- 

 tations characteristic of the different 

 genera. Such changes may be relatively 

 rapid, and for the same reason they count 

 for little from the standpoint of phylog- 

 eny. On the other hand, the non-useful 

 traits, the petty traits of form and colora- 

 tion which distinguish a species in Oahu 

 from its homologue in Kauai or Hawaii, 

 are results of isolation. These results 

 may be analyzed as in part differences in 

 selection with different competition, dif- 

 ferent food and different conditions, and in 

 part to hereditary difference due to the 

 personal eccentricities in the parent stock 

 from which the newer species was derived. 



In these and in all similar cases we may 

 confidently affirm : The adaptive characters 

 a species may present are due to natural 

 selection or are developed in connection 

 with the demands of competition. The 

 characters, non-adaptive, which chiefly dis- 

 tinguish species do not result from nat- 

 ural selection, but from some form of geo- 

 graphical isolation and the segregation of 

 individuals resulting from it. 



The origin of races and breeds of do- 

 mestic animals is in general of precisely 

 the same nature. In traveling over Eng- 

 land one is struck by the fact that each 

 county has its own breed of sheep, each of 

 these having its type of excellence in 

 mutton, wool, hardiness or fertility, but 



the breeds distinguished by characters 

 having no utility either to sheep or to man. 



The breeds are formed primarily by 

 isolation. The traits of the first individ- 

 uals in each region are intensified by 

 the in-breeding resulting from segrega- 

 tion. Natural selection preserves the har- 

 diest, the most docile and the most fertile ; 

 artificial selection those which yield the 

 most wool, the best mutton and the like. 

 The breed once established, artificial selec- 

 tion also tends to intensify and to preserve 

 its non-adaptive characteristic marks. The 

 more pride the breeders take in their stock, 

 the more certain is the preservation of the 

 breed's useless peculiarities. 



Taking the common middle-wool sheep of 

 southern England, the following key to 

 some of the visible race traits was made 

 while driving along the county roads. 



a. Rams and ewes with short white horns. Dor- 

 setshire. 

 na. No horns. 



6. Face and ears black. 



c. Skin below tail black. Hampshire. 

 CO. Skin below tail white. Devonshire. 

 bb. Face and legs tawny: no black. Southdown. 

 bbb. Face and ears white: ears erect. Cheviot. 



Not one of these characters has the 

 slightest intrinsic or physiological value. 

 Each of them would disappear in a few, 

 generations of crossing, and in each breed 

 the virtues of wool or of flesh exist wholly 

 independently of these race marks. 



Analogous to these race peculiarities of 

 sheep are the minor traits among the men 

 of different regions. Certain gradual 

 changes in speech are due to adaptation, 

 the fitness of the word for its purpose, 

 analogous to natural selection. The non- 

 adaptive matters of dialect find their origin 

 in the exigencies of isolation, while lan- 

 guages in general are explainable by the 

 combined facts of migration, isolation and 

 the adaptation of words for the direct uses 

 of speech. 



