EVOLUTION OF THE COLORS OF BIRDS. 225 



Mr. Charles Richmond informs me that the young female 

 often has the top of the head marked with yellow. Spec- 

 imens in the National Museum collection failed to 

 demonstrate this, as the sex of the young is in many 

 instances undetermined. This peculiar head marking 

 of the young seems to point to but one thing — to a 

 different and perhaps more highly developed ancestral 

 plumage. At any rate, the crown patch, which once 

 extended over the entire head, has now become restricted 

 to a comparatively narrow line across the nape. 



THE DIRECT INFLUENCES OF THE ENVIRONMENT. 



In the preceding discussion of the factors involved in 

 the evolution of the colors of North American birds, the 

 distribution of pigment in accordance with the internal 

 laws of growth was first considered, then the utility of 

 the various colors and their patterns, and the manner 

 in which natural selection had been instrumental in their 

 development, and finally beautiful colors, which had been 

 evolved by sexual selection, and the manner in which the 

 laws of heredity had tended to reproduce, first in the fe- 

 male, and afterwards in the young, at successively earlier 

 and earlier stages, in accordance with Cope's law of accel- 

 eration, the characters which had been acquired by the 

 male. We have yet to observe how these various mark- 

 ings may be modified by the direct action of the en- 

 vironment — by the influences of food, temperature, 

 moisture, etc. — in a way which is of no utility to the 

 species. If the results of environmental influence were 

 a detriment to the species, the race would either die out 

 or become adapted to the change, but if these direct in- 

 fluences were an advantage, they would be seized upon 

 by natural selection, and made the most of. 



Eimer considers that the part played by the direct in- 

 fluence of the environment in the evolution of colors is 

 15 



