History of the Theory of Heredity. 39 



that *'Iife is the continuous adjustment between inter- 

 nal relations and external relations." This, like Haeckel's 

 statement that heredity is memory, is not very clear 

 without explanation, but its meaning may perhaps be 

 brought out by an illustration. 



If I kick a stone I produce in it certain changes, such 

 as motion, heat, etc.; these changes being directly pro- 

 duced by the kick are simply manifestations of the 

 energy transferred from my foot to the stone. If, in- 

 stead of a stone, I kick a dog, I produce a similar set 

 of changes, and something more. The experience of 

 the dog and of his ancestors has taught him that such 

 yiolent attacks are always associated with a disposition 

 to commit still further violence, so, when the dog feels 

 the blow he immediately performs actions which have 

 as their object, escape from or avoidance of the danger 

 which he has not yet experienced, but which he knows 

 to be imminent. These actions are not the effect of the 

 kick, for the energy expended may be hundreds of times 

 greater. Their character is determined, not by any 

 change in the dog, but by the character, the disposition, 

 which he has inherited; and whether he retaliates by an 

 attack on his own part, puts his tail between his legs 

 and runs, or crouches at my feet, his actions are the 

 effect, not of the kick, but of j^ast experience as to the 

 best means of escaping further injury. There is a rela- 

 tion, external to the dog, between the kick and a dispo- 

 sition to injure the dog, and there is within the dog a 

 relation between the sensation of injury and the actions 

 which experience has shown to be the proper ones for 

 escaping further injury. 



That which distinguishes the dog from the stone is 

 the power to adjust these internal relations to the ex- 

 ternal relations, to conform his conduct to the laws of 



