ACQUIRED CHARACTERS DEFINED 143 



acquired characters are required to prove that a reaction, 

 which can only be started by an external force in the 

 parent, starts without this stimulus in the offspring. 



We owe another definition to Mr. Francis Galton : 

 ' Characters are said to be acquired, when they are 

 regularly found in those individuals only, who have been 

 subjected to certain special and abnormal conditions/ 1 



Professor Lloyd Morgan's definition conveys nearly the 

 same idea : — ' When the complex of stimuli, which con- 

 stitute the normal environment, are sufficiently altered (to 

 upset that balance established between environment and 

 innate qualities resulting in the production of a normal 

 individual) to produce an appreciable change, such a 

 modification or ' difference ' may be called an acquired 

 character.' 2 



Such results of abnormal conditions undoubtedly supply 

 extremely striking examples of acquired characters, but it 

 is, I submit, a mistake to make too much of abnormality, 

 or to import it into a definition. Some of the most 

 marked and certainly the most easily studied and tested 

 of acquired characters are the differences between the 

 effects of alternative environments, all of which are 

 normal, upon the individuals of a single species. The 

 green colour of a larva of Amphidasys betularia, if fed 

 upon broom, is an acquired character, as is the dark 

 colour it would assume upon oak, &c. I think therefore 

 that a more satisfactory definition of, at any rate, a large 

 class of acquired characters may be framed as follows : — 

 ' Whenever change in the environment regularly produces 

 appreciable change in an organism, such difference may 

 be called an acquired character.' 



Sir Edward Fry has objected to Mr. Galton's definition 

 — and his objection would equally apply to that which 

 I have suggested above — that 'the possibility of inheri- 

 tance is excluded by the definition, and the inquiry 

 whether acquired characters are inherited is impossible '. 3 



1 Nature, vol. li, 1894, p. 56. 



2 Baldwin's Dictionary of Philosophy and Psychology, vol. i, p. 10. 



3 Nature, vol. li, 1894, p. 198. See also Professor Lankester's reply 

 to the criticism, on p. 245. 



