INSTINCT 51 



teeth, nails, hair, and some other appendages, seem to 

 depend almost entirely with regard to their shape and 

 development upon nourishment, and are therefore inborn 

 characters. Almost everything else, however, is modified 

 by acquirement. The development of the muscles, the 

 growth of the bones, and the general form of the whole 

 organism in the higher animals, are modified by acquire- 

 ments. Some of these acquirements are as constant in the 

 race as the inborn characters. This is because all indi- 

 viduals are subjected to similar stimuli during their period 

 of growth. All children, unless prevented by disease or 

 accident, learn to walk and gratify the instinct to play, thus 

 producing similar acquirements in all normal individuals. 



The comparison between the higher and lower animals 

 makes this difference between inborn and acquired char- 

 acters clearer. In the vast majority of insects, for instance, 

 there are practically no acquired characters ; almost all of 

 them are inborn. Take the life-history of a moth or butter- 

 fly as an example. The caterpillar hatches out of the egg 

 complete in all its parts, and capable of looking after itself ; 

 directly it hatches out it simply grows in response to the 

 stimulus of nourishment. It does not acquire any know- 

 ledge with regard to the kind of food which is necessary for 

 its well-being ; it is born with this knowledge. When the 

 next stage in its life-history arrives, it spins itself a cocoon, 

 and that without ever having seen a cocoon. This know- 

 ledge and skill is an inborn character, and the caterpillar 

 is prompted to spin a cocoon at the proper time purely by 

 instinct. When in the cocoon, the caterpillar is metamor- 

 phosed into a chrysalis, and in the chrysalis all the parts 

 of the perfect butterfly or moth are developed simply by 

 growth. When the butterfly or moth hatches out in due 

 course, all its muscles and organs are developed, and it is 

 not dependent upon the stimulus of use, that is, of exercise 

 in the case of the muscles, for development. Here we see 

 nothing but inborn characters, and no acquired characters. 

 As we go up the scale of animal life, we find fewer inborn 



