12 Heredity and Social Progress 



tion that demands a new principle instead of 

 one that is known to be active in other cases. 



3. Not until an old principle fails to explain 

 all cases brought under it is it legitimate to 

 introduce a new principle. 



4. A basis of explanation in a known prin- 

 ciple is more valid than an explanation in- 

 volving an unknown principle. 



5. If a few elements are repeatedly used to 

 make a complex organism, it is highly prob- 

 able that all possible combinations have already 

 been made, and therefore it is also probable 

 that instances of every combination are in 

 existence or have existed. The presumption 

 of a general law is in favor of a hypothesis as 

 soon as single instances of its operation are 

 discovered. 



6. Links missing in the verification of a 

 chain of reasoning do not render a hypothe- 

 sis improbable. 



7. The principle of chance must never be 

 admitted. 



8. Whenever a specific form is found, varia- 

 tions from this form may be assumed. This is 

 involved in the theory of evolution by which 



