The Days of a Man 



D901 



Biological 

 friction 



sarily to eliminate or belittle any other factor. 

 Isolation is a condition, not a force; of itself it can do 

 nothing. It may be defined as biological friction, 

 the effect of impediments to free movement of in- 

 dividuals. Species change or diverge with space and 

 with time: with space, because geographical exten- 

 sion, including consequent barriers to interbreeding, 

 divides the stock and surrounds migrants with new 

 conditions; with time, because the progress of centu- 

 ries brings change in all environment. The begin- 

 ning of each new species rests on the variability of 

 individuals. 



Hawaiian 

 fuhes 



In 1899 Jenkins spent a successful summer on the 

 Islands, making the most important collection ob- 

 tained there up to that time — that is, 238 species, 

 78 of which were entirely new. The largest previous 

 collection, 117 species, was made in 1897 by Dr. Hugo 

 H. Schauinsland of Vienna, and described there in 

 1900 by Steindachner. But of these, only six were 

 new to science. With our extensive facilities we 

 brought in all of Jenkins' species as well as most of 

 those recorded by earlier writers. In our final report 

 (published in 1905) we listed 447 species of shore 

 fishes, 64 of them new, in addition to the 210 deep-sea 

 forms, all new, taken by Gilbert and his associates on 

 the Albatross in 1902. Of the 447, 232 have been 

 found nowhere else, although represented in Samoa, 

 Tahiti, and other places by geminate forms or ances- 

 tral types from which the far-flung Hawaiian species 

 are descended. But 142 of them occur also in Samoa 

 or Tahiti, 53 In southern Japan, 34 in the offshore 

 waters of Mexico; a few among them, allies of the 

 tuna and mackerel for the most part, are of course 



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