80 ESSAYS OF A BIOLOGIST 



comprising special symbols for particular external 

 objects, and thus making it possible to have a much 

 more detailed knowledge and classification of the 

 outer world. In the second place, he can frame ab- 

 stract ideas or concepts, and is thus enabled to 

 extract the general kernel from the husk of innumer- 

 able separate and different particulars. As a result 

 of these two faculties, he possesses what we may call 

 a new, accessory form of inheritance. True biolog- 

 ical inheritance takes place by means of the repro- 

 ductive cells. In some birds and mammals, the 

 behaviour of the young is modified by what they 

 learn from their parents, so that they profit by the 

 experience of their elders; however, this profiting by 

 experience is not cumulative, but must be repeated 

 afresh in each generation. In man, on the other 

 hand, speech and writing make it possible to con- 

 struct a continuous tradition, by means of which ex- 

 perience may be actually accumulated from genera- 

 tion to generation. There are thus two forms of 

 inheritance in man, two hereditary streams — biolog- 

 ical inheritance, by means of germ-cells or detached 

 portions of the organism, in which favourable 

 mutations may be accumulated by selection, and 

 "experience-inheritance,'' by means of tradition, in 

 which useful experience may be accumulated by the 

 activity of mind. By means of tradition-inheritance, 

 man is virtually enabled to "inherit acquired char- 

 acters"; thus the environment in which the latter 

 stages of his development are passed through, and 



