THE EVOLUTION OF THE COLORS OF NORTH AMER- 

 ICAN LAND BIRDS. 



I. Introduction. 



A few words of explanation may be said with regard to 

 the greatly disproportionate length of the introductory 

 portion of this work. To the uninitiated the most perfect 

 harmony is commonly thought to prevail concerning 

 the great problems of evolutionary philosophy, but once 

 within the circle of current scientific thought and the 

 reverse is found to be true. Instead of harmony, discord 

 is discovered. There is hardly one of the important 

 doctrines concerning which a consensus of scientific 

 opinion has been attained. To be sure, all maintain that 

 Darwinism or natural selection is a factor in evolution, 

 but while some hold it to be the only factor, and all-suffi- 

 cient in the creation of species, others believe it to be a 

 very minor agency, and relegate it to the post of inspec- 

 tor-general of the army of life. With regard to sexual se- 

 lection the same diversity of opinion prevails, one school 

 advocating sexual selection as the sole agent in produc- 

 ing the brilliant colors and varied plumes of male birds, 

 etc., the other extreme asserting that sexual selection as 

 a factor in evolution is a myth. Still greater is the di- 

 versity of opinion and more intense the feeling in regard 

 to that momentous question which is at present agitating 

 the troubled sea of scientific thought — the transmission 

 of acquired character. 



In view of all this disagreement, it is quite impossible 

 to undertake any general scientific investigations in the 

 field of evolution without a tolerably thorough survey of 

 the whole ground. With this end in view, and merely 

 as a preparation for the more particular investigations 

 of the work, these preliminary pages have been written. 

 The tenability* of the theories here advanced need not 



