November 24; 1905.] 



SCIENCE. 



667 



with many of my fellow-systematists, in 

 the evolution of species and races by en- 

 vironment, which, of course, includes evolu- 

 tion by isolation. This seems far more 

 rational than evolution by natural selec- 

 tion, as this process was originally defined. 

 But since the inefficiency of natural selec- 

 tion, pure and simple, to produce the re- 

 sults formerly attributed to it became evi- 

 dent the significance of the term has been 

 expanded to embrace evolution through 

 climatic influences, including also the fac- 

 tor of isolation. The inefficiency of nat- 

 ural selection, as originally defined, in the 

 evolution of species and races was the sub- 

 ject of frequent comment by the present 

 writer in various papers published some 

 thirty years ago, in opposition to which 

 was urged the direct action of environment 

 in the origination of incipient species. 

 The discussion was eventually summarized 

 in a paper published in 1877, entitled ' The 

 Influence of Physical Conditions in the 

 vlenesis of Species.' This paper, of some 

 thirty-three pages, appeared in a short- 

 lived and not widely known magazine,^ 

 and thus doubtless escaped the attention of 

 many investigators interested in such prob- 

 lems. The facts of geographic variation 

 were here presented at some length. 



In discussing Darwin's statement* re- 

 garding the method of the action of natural 

 selection, namely: 'I believe that natural 

 selection generally acts slowly in effecting 

 changes, at long intervals of time, and only 

 on a few of the inhahitants of the same 

 region,' the direct and simultaneous action 

 of climatic conditions upon all of the indi- 

 viduals inhabiting the same region was 

 dwelt upon at length. Thus, to quote a 

 few passages: 



The local races of any given region, as compared 

 collectively with those of contiguous regions, and 



^ The Radical Review, No. 1, May, 1877, pp. 

 108-140. 

 * ' Origin of Species,' 5th ed., p. 168. 



the manner of their mutual intergradation, point 

 plainly to some general or widely acting cause 

 of differentiation. This is indicated by the 

 constancy of the results, so many species, belong- 

 ing to numerous and widely distinct groups, being 

 similarly alTected. * * * There is, however, a 

 vast amount of unquestionable proof of the direct 

 and constant action of climate and other condi- 

 tions of life upon animals, and that such geo- 

 graphical variations as the thicker and softer fur 

 of mammals inhabiting cold regions, smaller size 

 and brighter colors at the southward, etc., do not 

 require the action of natural selection, in its 

 strict and proper sense, for their explanation. It 

 is well known, for instance, that a flock of fine- 

 wooled sheep, when taken to a hot climate, 

 rapidly acquire a coarser and coarser fleece, till, 

 in a few generations, it nearly loses its character 

 of proper wool, and becomes simply hair; that 

 the change affects simultaneously the whole flock, 

 and is not brought about by one or two individ- 

 uals acquiring a coarser fleece and through their 

 descendants modifying the character of the herd. 

 Furthermore, in the case of sheep, it is well 

 known that certain countries are very favorable 

 to the production of a fine fleece, and that fine- 

 wooled breeds, even by man's aid, can not be 

 perpetuated in other regions. Again, it is a fact 

 of common observation that in birds and mam- 

 mals colors become more or less faded toward the 

 moulting season simply by the direct action of the 

 elements — the tints of the fresh and the long- 

 worn plumage or pelage being more or less strik- 

 ingly different in the same individuals — and that 

 this contrast at different seasons is more marked 

 in arid than in moist regions, through the greater 

 bleaching effect of a dry heated atmosphere and the 

 more intense dazzling sunlight of regions that 

 are not only cloudless, but lack the protection 

 afforded by abundant vegetation. 



But climatic conditions were not claimed 

 in this essay as the only agent in the evolu- 

 tion of species and races. President Jor- 

 dan has referred to the song birds of the 

 family Drepanidte in the Hawaiian Islands, 

 with such remarkable diversity in the form 

 of the bill and other features, which he 

 ascribes, perhaps properly enough, in part 

 to natural selection and in part to isolation. 

 Upon such cases the following paragraph 

 from my long-forgotten paper has some 

 bearing : 



