CHAPTER X 



CONCLUSIONS 

 HEREDITY AND ENVIRONMENT. 



We can distinguish three stages in the evolution of every 

 science : First we have the period of bhnd speculation, 

 of fanciful metaphysical explanations, without the slightest 

 attempt to investigate or verify them. Then comes the 

 age of reaction — the time of studious collection of facts 

 and their careful classification — generally coupled with a 

 ruthless disdain of all theorizing. vSo far as the systematiza- 

 tion of knowledge goes, it forms the absolutely essential 

 spade-work for all sciences — a very necessary and laborious 

 undertaking. But a science, to be " knowledge " in the 

 real sense of the word, must be more than a mere collection 

 of facts. It must furnish us with practical solutions for 

 purposes of everyday life ; it must not only be able to tell, 

 but also to foretell. In other words, a science, in order 

 to become a real science, must contain certain leading 

 principles, serving at the same time as a unifying bond of 

 the organized knowledge and giving us working ideas for 

 our guidance in practical life. 



It is not going too far to assert that the Science of 

 Heredity has just entered into its third phase. In the 

 mass of conflicting statements and hypotheses certain facts 

 have come to stand out with sufficient clearness to afford 

 us light enough to see the direction in which we have to 

 travel. And be it understood and impressed once more : 

 Procreation being the foundation of all life, the science of 

 heredity forms the basis of the science of life, and its 



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