lOO Instinct. 



certainty ; but the need arising from certain condi- 

 tions does not in any manner account for the origin 

 of the impulse to do a given thing, or the marvel- 

 lous skill often manifested to meet the conditions 

 which the necessity imposes. 



If we consider the nests of birds for instance, 

 which are the animal homes best known to us, they 

 nearly all are made simply for the care of the young; 

 but no one could tell from the examination of a 

 bird, what materials it v/ould select for its nest, its 

 method of combining them or the position of the 

 nest. Birds very nearly allied differ much in their 

 habits of nesting, and yet in each case the nest is so 

 uniform in its structure and surroundings as to be 

 in general characteristic of the species. That is, 

 birds of the same species, under the same circum- 

 stances, build with like m.aterials and in like posi- 

 tions. Any departure from the common method 

 of building in any given locality will be found, on 

 careful examination, to be very slight, and to be so 

 uniform in the variation, according to the surround- 

 ing conditions, as to appear to be a manifestation 

 of a wider range of Instinct than had generally been 

 attributed to the bird, rather than a result of intel- 

 ligent contrivance, as is seen among men. The va- 

 riation in the form of nest once seen can be described 

 as the certain work of the animal when circum- 

 stances demand or favor the change ; the new man- 

 ifestation of instinctive knowledge and skill being 

 made in a specific method to meet the new condi- 

 tions. 



We need only call attention to a few of our well 



