EVOLUTION AND NATURAL SELECTION 11 



for believing that they are only contrasted aspects of the same 

 phenomenon. For stability of species is due to survival in the 

 same way that mutabiUty is. 



Evolution and Instinct 



An action which requires experience to enable us to perform 

 it, says Darwin, when performed by an animal, more espe- 

 cially by a very young one without experience, and when per- 

 formed by many individuals in the sanie way without their 

 knowing for what purpose it is performed, is usually said to be 

 instinctive. A little dose of judgment or reason, says Huber, 

 often comes into play even with animals low in the scale of 

 life. Instinct has been defined as hereditary habit (behavior), 

 comprising an element of transmitted experience. In all 

 ca.ses where instinct becomes complex or refined we seem com- 

 pelled to accept the view that its origin is to be sought in con- 

 sciously intelligent adjustment on the part of the ancestors. 

 Many of the lower animals exhibit instinctive actions, such, 

 for instance, as a spider ■ spinning its web, a bird building its 

 nest, and the beaver building a dam, these actions being per- 

 fornied the first time the animal tries almost as well as when 

 it is older and experienced. Spencer supposed that intelli- 

 gence first arose through the multiplication and coordination 

 of reflex actions, and although many of the simple instincts 

 grade into reflex actions, and can hardly be distinguished from 

 them, yet the more complex instincts seem to have arisen inde- 

 pendently of intelligence. Instinct has been described as being 

 automatic obedience to the demands of external conditions. 

 As these conditions vary with each kind of animal, so must 

 the demand vary, and from this arises the great variety actually 

 seen in the instincts of different animals. With others, instinct 

 has been regarded as the natural survival of those methods of 

 automatic response which were most useful to the life of the 

 animal, the individuals having less effective methods of reflex 

 action having perished, leaving no offspring. 



As the mental qualities of animals vary and as instincts 

 vary sUghtly in a state of nature, and as instincts are of the 

 highest importance to each animal, there is no real difficulty 

 under changing conditions of hfe, says Darwin, in "natural 



