LECTURE VI 



MIGRATION IN ITS BEARING ON LAMARCKISM 



In the last lecture I tried to show that the adaptations of 

 nature are primarily for the good of the species ; that they are 

 beneficial to individuals only so far as these individuals are essen- 

 tial to the welfare of the species ; and that they often are inju- 

 rious or destructive to the individual. I also pointed out that, 

 since this is so, the nurture of the individual does not seem to 

 have any bearing upon the origin of adaptation. 



To my mind, no illustration of this great natural law is more 

 simple or more easy to understand, than that afforded by some of 

 the phenomena of migration. 



The young salmon which is born in a mountain stream is 

 soon impelled, by something in its nature, to journey downward, 

 often many hundred miles, until it reaches the unknown ocean, 

 where it would discover, if it had faculties for anything so sub- 

 jective as discovery, that, while it was born in a mountain stream, 

 it was made for life in the great ocean. 



It has brought from its mountain home a natural aptitude for 

 eluding all the strange enemies, and for avoiding all the novel 

 dangers, which it finds in this new world; and it leads an active 

 predatory life, fiercely pursuing and destroying its natural, but 

 previously unknown, prey ; growing rapidly ; quickly acquiring all 

 the characteristics of the adult salmon ; and storing up the intense 

 nervous energy, and the muscular strength, which will be needed 

 for forcing its way up the rapids in the mountain torrents, leap- 

 ing waterfalls, and fighting for its passage, where it had, long 

 ago, darted down with the current. As sexual maturity ap- 

 proaches, some stimulus, which has its origin in the developing 



1 Reprinted with slight changes from the Popular Science Monthly. April, 1898. 



