THE QUALITATIVE PROBLEM 323 



As history ceases to be strictly correlated with changes in quality, 

 it comes to be influenced by a factor the nature and strength of 

 which is largely determined by the quantity of population. Thus 

 the two aspects of the whole problem are linked together in the 

 case of man in a manner that does not obtain among species in 

 a state of nature. 



The attempt to deal with this problem will be undertaken in 

 the following manner. In Chapter III reference was made to the 

 influence of the environment upon growth and upon the adult form. 

 In Chapter XIV this subject will be developed so far as species 

 in a state of nature are concerned, and the results of the inquiry 

 will be applied to man in Chapter XV. The subject-matter of 

 Chapter XV will be confined to the influence of the environment 

 upon human bodily and mental characters. The influence of the 

 environment as a stimulus affecting the direction in which mental 

 characters are used will be left to a future chapter. 



We next turn to inquire what influence changes in the germ- 

 cells have had. Before we can make any progress it is necessary 

 to ask what characters — physical and mental — have their basis 

 in the germ-cells, and an inquiry into this subject will occi^y 

 Chapter XVI. In Chapters XVII and XVIII we ask what 

 evidence there is of selection and other factors throughout human 

 history which we have reason to suppose have a bearing on 

 change in the average germinal constitution of the human species. 

 This will among other things necessitate an examination of the facts 

 in Chapters VII, VIII, and X in order to ascertain what bearing 

 they have upon selection- Having thus some knowledge of what 

 is inherited, and having discussed the occurrence of such factors 

 as in human history may have brought about changes from one 

 generation to another in the character inherited, we shall be in 

 a position in Chapter XVII to attempt an estimate of the results 

 which the factors — selection and others — have had upon physical 

 characters. We shall find that as regards these characters the 

 position is more or less clear ; we shall find, that is to say, that 

 the influence of selection and other factors, considered in con- 

 junction with the influence of the environment discussed in 

 Chapter XV, does enable us in the main to understand how the 

 physical evolution of man has come about. With regard to 

 mental characters to be discussed in Chapter XVIII, we shall 

 find that the task cannot be similarly completed. With a far less 



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