ORIGIN OF LAKE SALMON. 143 



region, but in a neighboring district separated from the first by a barrier of some sort, or 

 at least by a barrier of country, the breadth of which gives the effect of a barrier.' 



As I understand it this does not signify that two closely related species never occur 

 now in the same locality but that they were evolved under somewhat different con- 

 ditions through isolation, and when found in the same locality it is due to the later 

 advent of one of them. As the Law indicates, the barrier may be one of distance, and 

 Jordan (1929, p. ix) has also said that 'most of our species are plainly related to geo- 

 graphical influences, or rather obstacles. The presence of barriers of mountain, sea, 

 prairie, or desert, or of cUmate, food, or enemies, limits the range of forms.' 



As has been previously suggested, the barriers or obstacles effecting the divergence or 

 separation of the closely related chars, trout, and salmons, were largely climate, and 

 distance, with attendant conditions. A theory previously advanced was to the effect 

 that chars, trouts and salmons were not evolved under the same conditions or in the 

 same latitudinal range. Without entering into a prolonged repetition of the theory, it 

 may be said that the chars are the result of adaptation to more rigorous changes of 

 conditions than were the trouts and salmons as indicated by their present distribution 

 and the conditions of their habitats. In their structure and distribution, the trouts 

 appear to have been subjected to less rigorous conditions and the salmons to have been 

 the least affected, and these later were the latest to attain their present distribution. 



As pertains to the evolution of the chars, trout, and salmons there seems to be no 

 necessity for regarding the trouts and salmons as having been governed by natural 

 laws different from those affecting the chars. The factors concerned differed only in 

 degree. This is implied, although not definitely so stated, in the suggestion offered by 

 the editor of the Salmon and Trout Magazine, previously quoted. It is a logical con- 

 clusion that the 'landlocking' of the salmon occurred in something the same way as of 

 the chars and trouts. All three forms originated in somewhat different environmental 

 conditions. And if Jordan's Law holds with the fish in the sea, they could not have 

 originated in the same region, and the same may be said of the sea salmon and lake 

 salmon. 



Doubtless, during the glacial period the range of the primitive salmon stock was much 

 farther south than that of the char stock, and broadly speaking, the trout stock was 

 intermediate in its range. With the recession of the ice the ranges moved northward, 

 each became adapted to the particular conditions within its range, and in the case of the 

 salmon, the most northern section came in contact with the greater amount of cold, 

 fresh water, which they frequented for food and reproduction. To repeat, they became 

 adapted to those particular conditions. With the elevation of the land the expanses of 

 brackish and fresh water contracted and the fish were isolated by force of their adapta- 

 tion and the 'barrier' of warmer and more sahne waters of the sea. There they had to 

 remain, not on account of dams, natural or artificial, not because they 'forgot to go to 

 sea,' as Tomah, Dr. Hamlin's Indian guide said (Hamlin 1874, p. 341), but perhaps, 

 to paraphrase the words of Hallock (1877, p. 306) it could not go to sea if it would. 

 Through physiological adaptation and heredity they had become fresh-water salmon. 



