MIGRATION IN ITS BEARING ON LAMARCKISM I17 



the birds are, in themselves, a sufficient explanation of all the 

 broader and more general characteristics of migration. 



It seems much more simple, and much more consistent with 

 our knowledge of the past history of living things, in general, to 

 ^^Bieve it had its origin in an intense but geographically indefinite 

 impulse, which led birds to scatter at the breeding season, and to 

 hunt out safe hiding places for their nests, and that, as enemies 

 also improved in power to find the most accessible nests, the 

 instinct gradually shaped itself into definiteness through selection 

 and extermination, until, at last, safe breeding grounds far away 

 from home, and far away from the enemies which there abounded, 

 have become . established, and until many species and all the sur- 

 viving members of each species have come to share the impulse 

 to resort to these selected breeding places on the approach of the 

 period of sexual excitement, and to follow the same path between 

 points far apart ; that the increasing safety of the eggs and young 

 has permitted a low birth-rate, and the improvement by selection 

 of the power of rapid and long-continued flight ; and that this has, 

 in its turn, permitted the migration to become longer and longer, 

 and more and more protective to the eggs and young. 



The history of migratory birds has been long and complicated ; 

 and there has been time for great changes in the distribution of 

 land and water, and for changes of climate, and these have, no 

 doubt, left some permanent impression on the habits of birds. 



They have not eluded all their enemies, for predaceous birds and 

 their prey are found together in both the summer and the winter 

 homes. New ways to escape enemies and new ways to find food 

 are as important as they ever were, and birds undoubtedly have 

 capacity for improving by experience and for forming new habits. 



All these influences have, no doubt, had and still have, their 

 effect on migration, so that the history of the subject is very 

 complicated; although it seems clear that its broader outlines 

 admit of explanation by natural selection without recourse to 

 geology or to the inheritance of the direct effects of nurture. 



In conclusion I wish to remind the reader that our present 

 interest in migration lies in its value as an illustration of the 

 general law that the adaptations of nature are for the good of 

 the species and not for the benefit of the individual. This law 



