### Clue: In Darwin's study he tried out theory at last (8)
### Answer: HEREDITY 
 ### Explanation: Definition: In Darwin's study
  Anagram(*out*) of HE TRIED + Y(last letter,*at last* of *theory*).  Defn:  *In* evolution, *Darwin's* field of *study*, the mechanism by which changes in characteristics are handed down through the generations; although, during his time, Darwin didn't know much about how heredity worked.  An &lit I think