664 ^^^ POPULAR SCIENCE MONTHLY. 



row, the liabits necessary for successful struggle for life r\(n in few 

 lines, and these lines become deepened with every generation, until 

 they become, as it were, petrified in brain-structure. 



Instinct, therefore, is accumukited experience, or knowledge of 

 many generations fixed permanently and petrified in brain-structure. 

 All such petrifaction arrests development, because unadaptable to 

 new conditions. They are found, therefore, only in classes and fami- 

 lies widely differentiated from the main stem of evolution, from tlie 

 lowest animals to man. Instincts are, indeed, the flower and fruit at 

 the end of these widely-ditferentiated branches, but flowering and 

 fruiting arrest onward growth. 



Now, there is also a social evolution. The organic evolution, which 

 found its term in man, is continued by man in social evolution. It is 

 natural, therefore, to look for the corresponding phenomenon in the 

 higher sphere of social evolution. I believe we find it in the phe- 

 nomenon of arrested civilizations, of which nearly all barbarous and 

 semi-civilized races are examples, but the Chinese and Japanese are 

 the most conspicuous ; and also, perhaps, to some extent, in the phe- 

 nomenon of dead civilizations, of which the Greek and Roman are the 

 most conspicuous. Nations isolated and breeding true, i. e., without 

 mixture with other nations, gradually assume fixed customs and hab- 

 its which become enforced, and therefore perpetuated by law, and 

 ^nvCAy petrified in national character. The result is often marvelous 

 development, but extremely limited. Here, again, perfect flower and 

 fruit destroy growth. Here again, also, it occurs in a type or branch 

 widely differentiated from the main stem of social progress. This ex- 

 plains one of the advantages of cross-breeding, or mixing of varieties 

 within certain limits of national varieties, if not of races.' It confers 

 plasticity ; it prevents the formation of fixed national character, and 

 the consequent arrest of progress by petrifaction. 



Let us hope, then, that the growing tree of society will always 

 remain an excurrent ; that its upshooting stem shall never lose itself 

 in mere branches; that its terminal bud shall never fail, but always 

 continue to groAV. Its branches may flower, and fruit, and die, or 

 cease to grow, but the trunk stretches ever upward and bears each 

 successive flowering branch higher and still higher. Doubtless the 

 ideal of humanity is that all right actions are spontaneously or instinc- 

 tively performed, and all important truths intuitively or instinctively 

 known ; but this is and must be an unattainable ideal ; for, this con- 

 dition reached, how shall we any longer aspire? the terminal bud 

 flowering, how shall the tree continue to grow ? Human nature must 

 never petrify into instinct; inherited wealth must never supersede 

 the necessity of individual acquirement. 



' The effect of mixing varieties requires careful investigation, for it is yet very im- 

 perfectly understood. There seems little doubt, however, that there is a limit beyond 

 which varieties do not mix with improvement. 



