CHAPTER V. 



THE TURTLE-DOVE PATTERN IN THE PHYLOGENY OF PIGEONS. 1 



But the causes and conditions of variation have yet to be thoroughly explored; and the 

 importance of natural selection will not be impaired, even if further inquiries should prove that 

 variability is definite and is determined in certain directions rather than in others, by conditions 

 inherent in that which varies. It is quite conceivable that every species tends to produce varieties 

 of a limited number and kind and that the effect of natural selection is to favor the development 

 of some of these, while it opposes the development of others along their predetermined lines of 

 modification. (Huxley, Darwiniana, p. 223.) 



GENERAL STATEMENT. 



Color and color-marks present a wide range of the most puzzling problems— 

 the shades of the ground-color, the endless diversity of specific color-marks, the 

 distribution of color and color-marks geographically, their age sequences, regional 

 differentiations, form metamorphoses, sexual correlations, seasonal changes, pro- 

 tective adaptations, irregularity, lawlessness, non-amenability, non-conformity to 

 laws of heredity. 



What, at first thought, could appear more insignificant than a simple color-mark 

 of a feather? Can such lifeless surface-characters leatl us directly to central problems 

 in evolution — problems which involve at once variability, adaptation, heredity, the 

 genesis of species, and progressive development? Is not variation here too profuse, 

 too multifarious, too lawless to serve as safe ground for fruitful comparative studies 

 and reliable experimental tests? Such, very likely, might be one's first impressions. 

 As we inquire into the subject more closely, we shall see room for a more favorable 

 judgment. 



Where and how shall we study variation, if not in that which exhibits it abun- 

 dantly? Great variation in outward expression implies a correspondingly high 

 grade of plasticity in the internal foundations of such manifestation. Whether we 

 imagine that each mode and degree of expression has its special primordium, or 

 prefer to refer all the various expressions to one common germ-substance, it is 

 obvious enough that in these color-marks and the patterns which they form we 

 have a wide-ranging variability to deal with, with endless opportunity for both 

 natural and artificial selection and for experimentation. 



If the very exuberance that confronts one in the feathered world be somewhat 

 appalling on first approach, it costs but little effort to see that it all counts in favor 

 of the investigator. The greater the variability, the closer, in general, will be the 

 connections between stages, and the easier it will be to catch the trend of phyletic 

 derivation and to discover the common points of departure for whole groups of 

 related color-patterns, and possibly to reduce these points to a single point of depart- 

 ure for the whole bird kingdom. Such a vista, once opened, would orient the whole 



1 The arrangement of the several "groups" <>l materials of the chapters dealing with this subject is that of the 

 editor. Little of these materials was put into finished form by the author, and it has not been thought advisable 

 to make extensive changes in the record as found. The amount of textual matter is, at, many points, more limited 

 than is desirable. The statements here given — supplemented by the several very full considerations of previous 

 chapters — will, however, doubtless prove sufficient to guide the reader through the great number of illustrations. 

 Further, the legends accompanying the plates are often so full and complete as to render text less essential. The 

 plates and figures, if given alone, would go far toward accomplishing the aim of these chapters, namely, to show that 

 the most divergent forms — of pigeons, and of still other groups of birds —exhibit one or another stage or degree of 

 transformation of an identified ancestral color-pattern. — Ed. 

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