1893.] Recent Literature. 547 
RECENT LITERATURE. 
Evolution of the Colors of North American Land 
Birds.'—This octavo of 361 pages, published by the California 
Academy of Sciences, the author Mr. Charles A. Keeler, modestly 
calls a study. The views set forth are more or less provisional and 
tentative, and are intended to direct research into this new field of 
ornithological inquiry. The subject-matter of the essay is preceded by 
a discussion of the various views held as to the laws conditioning 
evolution, such as inheritance of acquired characters ; the nature of 
species ; natural and sexual selection, and isolation, as factors in the 
evolution of species. In concluding this rather lengthy introduction, 
the author remarks “ that life has evolved in accordance with tolerably 
definite and unvarying laws, and that the element of chance, if any 
such there be, is a very limited one.” 
In Part II the colors of North American birds, are treated of under 
the following heads: Modes of plumage changes; General principles 
of color in Birds ; The proportion and distribution of the colors in the 
North American genera; The pattern of markings; Variation of color 
with sex, age and season; The direct influences of the environment ; 
Geographical distribution as a factor in the evolution of colors; Orders, 
families and genera of North American Birds, considered from the 
stand-point of their evolution. 
The theory of bird colors which Mr. Keeler seeks to establish is as 
follows: Pigment is a chemical composition thrown off from the sys- 
tem of the bird, probably as a product of waste, and lodged in the 
integument. The chemical substance thus generated varies in different 
groups of birds, but is probably generally constant in the species of 
one genus, or frequently in an entire family. A certain genus would 
thus be capable of generating only a given number of fundamental 
colors, but natural and sexual selection by combining and rearranging 
this limited assortment can produce a variety of effects. : 
Associated with this theory is the Law of Assortment of Pigments ; 
that is, that the primitive color is a composite which, when more or less 
completely resolved into its component elements gives the specialized 
tints of the species or genus. If the system of the bird from which 
1Evolution of the Colors af North American Land Birds. Occasional Papers of the 
California Academy of Sciences III. By Charles A. Keeler. San Francisco, Jan- 
uary, 1893. 
