The Origin of Speci 



with some security the duration of these intervals 

 by a comparison of the preceding and succeeding 

 organic forms. We must be cautious in attempt- 

 ing to correlate as strictly contemporaneous two 

 formations, which do not include many identical 

 species, by the general succession of the forms of 

 life. 



As species are produced and exterminated by 

 slowly acting and still existing causes, and not by 

 miraculous acts of creation; and as the most im- 

 portant of all causes of organic change is one which 

 is almost independent of altered and perhaps 

 suddenly altered physical conditions, namely, 

 the mutual relation of organism to organism — 

 the improvement of one organism entailing t he- 

 improvement or the extermination of others; it 

 follows, that the amount of organic change in 

 the fossils of consecutive formations probablv 

 serves as a fair measure of the relative, though 

 not actual lapse of time. A number of sp< 

 however, keeping in a body might remain for a 

 long period unchanged, while within the same 

 period, several of these species, by migrating into • 

 new countries and coming into competition with 

 foreign associates, might become modified; so 

 that we must not overrate the accuracy of organic 

 change as a measure of time. 



In the future I see open fields for far more 

 important researches. Psychology will be se- 

 curely based on the foundation already well laid 

 by Mr. Herbert Spencer, that of the necessary 

 acquirement of each mental power and capacity 

 31 



