Nest-building, Incubation, and Migration. 233 



rendered definite through intelligent imitation? Is the 

 habit transmitted through organic inheritance, or handed 

 on through the influence of tradition ? Mr. Wallace has 

 advocated the latter view — at least, so far as specific 

 definiteness is concerned. On his view, if I rightly interpret 

 it, a bird may inherit an indefinite tendency to exercise 

 its- energies in building ; but how it builds depends upon 

 the tradition of its species. Exclude imitation, and they 

 no longer built a typical nest. Thus chaffinches taken to 

 New Zealand, and turned loose there, built nests which 

 bore " some resemblance to those of the hang-birds 

 (Icterida), with the exception that the cavity is at the top. 

 Clearly these New Zealand chaffinches," says Mr. Dixon,* 

 to whom we owe the observation, " were at a loss for a 

 design when fabricating their nest. They had no standard 

 to work by, no nests of their own kind to copy, no older 

 birds to give them any instruction, and the result is the 

 abnormal structure." 



Mr. Wallace quotes this under the heading of " varia- 

 tions of the habits of animals." It would be well to 

 restrict the term " variations " to departures of congenital 

 origin, and to apply the term " modifications" t to those 

 departures which are individually acquired. According to 

 those, who are unable to accept the inheritance of ac- 

 quired characters, of whom Mr. Wallace is one, the two 

 modes of departure from the activities normal to the 

 species are of very different value. Modifications, since 

 they are acquired, are not on this view inherited, and can 

 play no part in the development of instinct ; while varia- 

 tions are those departures which by natural selection can 

 be rendered definite and stereotyped as instincts. This, 



* Nature, vol. xxxi. p. 553. Quoted in "Darwinism," p. 76. 1 

 t Prof. Mark Baldwin adopts this usage in his paper on " A New Factor 

 in Evolution," in tbe American Naturalist for July, 1836. 



