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SCIENCE. 



[N. S. Vol. XXII. No. 566. 



produce and enforce adaptation to condi- 

 tions of life, the traits which distinguish 

 species bear little relation to utility. The 

 individuals which, separated from the main 

 flock, people an island, give their actual 

 traits to their actual descendants, and the 

 traits enforced by natural selection differ 

 from island. to island. If external condi- 

 tions were alike in all the islands the prog- 

 ress of evolution would perhaps run parallel 

 in all of them, and the only differences 

 which would persist would be derived from 

 differences in the parent stock. As some 

 difference in environment exists, there is a 

 corresponding difference in the species as a 

 result of adaptation. If great differences 

 in conditions exist, the change in the species 

 may be greater, more rapidly accomplished, 

 and the characters observed will bear a 

 closer relation to the principle of utility. 



Doubtless wide fluctuations or mutations 

 in every species are more common than we 

 suppose. "With free access to the mass of 

 the species, these are lost through inter- 

 breeding. Isolate them as in a garden or 

 an enclosure or on an island, and these may 

 be continued and intensified to form new 

 species or races. Any horticulturist will 

 illustrate this. 



At the risk of becoming tedious we must 

 continue these illustrations. The conten- 

 tion is not that species are occasionally as- 

 sociated with physical barriers, which de- 

 termine their range, and which have been 

 factors in their formation. It may be 

 claimed that such conditions are virtually 

 universal. When the geographical origin 

 of a species can not be shown it is because 

 the species has not been critically studied, 

 from absence of material or from absence 

 of interest on the part of naturalists, this 

 showing itself often in a semi-contemptuous 

 attitude of morphologists and physiologists 

 towards species mongers and towards out- 

 door students of nature generally. In a 

 few cases, a species ranges widely over the 



earth, showing little change in varying con- 

 ditions and little susceptibility to the re- 

 sults of isolation. In other cases, there is 

 some possibility that saltations, or suddenly 

 appearing characters, may give rise to a 

 new species within the territory already 

 occupied by the parent form. But these 

 cases are so rare that in ornithology, mam- 

 malogy, herpetology, conchology and ento- 

 mology, they are treated as negligible quan- 

 tities. In the distribution of fishes the 

 same rules hold good, but as the material 

 for study is relatively far less extensive 

 and less perfectly preserved than with 

 birds and insects, we have correspondingly 

 less certainty as to the actual traits of 

 species and subspecies, and the actual rela- 

 tion of these to the intervening barriers. 



The American genus Zonotriclvia com- 

 prises the group of streaked finches known 

 as white crowned sparrows. Most of these 

 agree in their grayish brown coloration, 

 streaked with darker brown, with two black 

 stripes on the crown of the head, the wings 

 with two white bars and tail without white 

 feathers. The wings and tail are long, the 

 bill small, and there is little else to separate 

 them from the great body of streaked spar- 

 rows, amidst which the white-crowned 

 stand as among the largest in size. 



In most of the group the crown of the 

 head is whitish between the two black 

 stripes. In one group of these there is no 

 yellow on the head, these being the typical 

 white crown sparrows, Zonotrichia leuco- 

 phrys. The common form breeds in the 

 Rocky Mountain region and northeastward 

 to Labrador. It has a black patch or stripe 

 before the eye. Northwestward, from Mon- 

 tana to Alaska, these sparrows have the 

 space before the eye whitish. These are 

 Zonotrichia leucopJirys gamheli. South- 

 ward, coastwise, from Vancouver Island to 

 Monterey, California, the edge of the wing 

 becomes yellow and we have Zoyiotrichia 

 leucopJirys nuttalli. 



