78 ESSAYS OF A BIOLOGIST 



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 abstract 

 ideas or concepts, and is thus enabled to extract the 

 general kernel from the husk of innumerable separate 

 and different particulars. As a result of these two 

 faculties, he possesses what we may call a new, acces- 

 sory form of inheritance. True biological inherit- 

 ance takes place by means of the reproductive 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 construct a continuous 

 tradition, by means of which experience may be 

 actually accumulated from generation to generation. 

 There are thus two forms of inheritance in man, 

 two hereditary streams — biological inheritance, by 

 means of germ-cells or detached portions of the 

 organism, in which favourable mutations may be 

 accumulated by selection, and ' experience-inherit- 

 ance,' 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 characters ' ; thus the environ- 

 ment in which the latter stages of his development are 

 passed through, and consequently his adult self, the 



