110 BEHAVIOR OF PIGEONS. 



nesting activities be manifested when they are useless, these consequences are 

 insignificant from the standpoint of the birds, and they do not occur with sufficient 

 frequency to militate against the practical utility of the bird's organization in the 

 long run. 



The instinctive organization, however, does possess a high degree of plasticity 

 and adaptiveness at many points. Acts are adapted to meet novel conditions and 

 the bird may persist in its duties in spite of many defects. The mating preferences 

 are quite plastic. Natural preferences may be overcome and a bird will pair with 

 a member of another species or with one of its own sex. Each bird may assume 

 the duties of the opposite sex throughout the cycle whenever necessary. The old 

 nest and site may be adopted in spite of a strong inclination to the contrary. 

 Continuous incubation may be attempted when the mate deserts. Incubation 

 will be continued in spite of serious defects and obstacles. Acts may be modified 

 to some degree by experience. The effect of experience has been noted chiefly in 

 connection with the mating preference, the preliminary symptoms of egg-laying, 

 the preference for a nesting-site, and the removal of fear and distrust of strange 

 birds. The effect of experience in mating has been discussed. It is remarked 

 (Chapter VII) that the female of the passenger-ring-dove pair "will learn by experi- 

 ence to waste less time in fruitless formalities, and make less ado over such a small 

 matter as laying an egg." The supposed male of "pair D" was driven from his nest 

 and then sat for a time in an empty box. In a few hours he developed a preference 

 for this site which was difficult to break, although the box contained no eggs and 

 was filled with dry dung. 



The author has developed what one may term an orthogenetic conception of 

 instinctive development. Instincts are not novel and unique constructions which 

 spring, without ancestry, into being; rather each new instinct 1 is but a slight 

 modification or organization of tendencies already in existence. This conception 

 is well depicted in his treatment of the phylogeny of incubation (Chapter VIII). 

 Each of the prior elements or stages in the process of development has its own 

 meaning and survival value. Any complicated instinct is built up by small incre- 

 ments; but natural selection is operative throughout, for each stage as well as the 

 final product has a selective utility of its own. The mutation conception is thus 

 unnecessary, and we are relieved of the difficulty of assuming a gradual or inte- 

 grative development over long periods in which natural selection is powerless to 

 operate. On this conception the same act with slight modifications may function 

 in widely different situations, and any act may have several utilitarian results. 

 The consequences bringing satisfaction to the bird may be far different from 

 those upon which natural selection has operated. Many illustrations are given 

 in the manuscripts. A pertinent example is the case of "billing," which occurs 

 in both courtship and feeding. There is a marked similarity and intimacy of con- 

 nection between charging and driving, display, jealousy, pugnacity, and the 

 behavior subsequent to dismounting. For the details of these relations the reader 

 is referred to the appropriate topics. 



1 In Chapter XIII this same principle is applied also to "intelligence." 



