34 SOCIAL HEREDITY AND SOCIAL EVOLUTION 



not wait for the slow process of learning in order to 

 live its life with, success. Social inheritance may be 

 of great moment in a long-lived race, but can be of 

 little significance in a short-lived species. Animals 

 whose whole life is passed in a few days or weeks 

 cannot wait for the slow process of learning, but must 

 depend upon something quicker. Hence we find 

 short-lived animals endowed with instincts which 

 come from organic inheritance. Now, instincts are 

 unquestionably the result of an inherited structure 

 of the nervous system. Two eggs are hatched under 

 the same hen and therefore under like conditions ; but 

 one hatches into a duck and runs to the water while 

 the other hatches into a chick and shuns it. No other 

 conclusion is possible except that the nervous system 

 that controls the muscle action is different in the 

 two cases. Our psychologists too are equally con- 

 fident that the nervous structure of the brain of a 

 child is different from that of an adult, and that it is, 

 moreover, different in the case of adult men in differ- 

 ent conditions. The brain of Newton at his zenith 

 was different in structure from that of Nero. The 

 human brain thus becomes molded by experience. 

 But in the life of a chick there is not time enough 

 in its few months of existence for the brain to be 

 molded by experience, and the animal is born with its 

 brain already preformed so as to control its actions. 

 We call the actions of the preformed brain by the 

 name of instincts, and we learn that the traits so 

 named are handed on from generation to genera- 

 tion by organic inheritance. We call the actions 

 of the brain that becomes molded by experience, 

 but is not preformed, by the name of intelligence, 

 and we find that this is not handed on by heredity 



