AS THE BIOLOGIST SEES IT 



heredity of specific unit characters. Not 

 all traits are inherited according to the 

 Mendelian order, but many are. This 

 order can be found out if it exists and 

 then predicted. 



It must be found out by experiment 

 (in lower animals and plants) or observa- 

 tion (in human beings) for each specific 

 trait in each species of plant and animal 

 and for man. The order cannot be 

 predicted for another species on the 

 basis of knowledge in one species; nor for 

 man on a basis of knowledge in lower 

 animals. The inheritance of each trait is 

 independent of the inheritance of any 

 other trait, with the exception of occa- 

 sional yoked or grouped traits which 

 behave as a single unit. It is unit inheri- 

 tance where single characteristics are the 

 units, not fractional inheritance where all 

 the traits or the whole individual is the 

 unit. It will take a long time to work out 

 the order of heredity for all the Mendeliz- 

 ing traits, physical and mental, which 

 the human species possesses, but it can be 

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