INTRODUCTION 5 



No one would suggest that even if the eggs were 

 incubated at different temperatures the single comb 

 would be altered to a rose comb. 



Clearl}', then, some characters are produced by an 

 environmental stimulus and others are determined 

 by inheritance, although in both cases interaction 

 of organism and environment takes place in the 

 development of the character. A given character 

 may occur in either or both categories. Thus fascia- 

 tion or flattening of the stem in plants usually results 

 from over-nutrition and is then, as a rule at least, 

 not inherited at all. But in Celosia cristata, the 

 coxcomb of gardens, extreme fasciation is a specific 

 character, distinguishing this form from C. pluniosa. 

 Again, thickening of the epidermis or formation of 

 corns results from friction of the skin of the hands or 

 feet, and is not inherited. But keratosis is an inherited 

 condition in which there is abnormal thickening of 

 the skin without any excessive friction. 



When a new character appears through a variation, 

 the first question one asks is whether it is inherited. 

 It is impossible to determine this with certainty 

 except by experiment — i.e., by breeding from the new 

 type. If it is inherited, one must conclude that a 

 germinal change has taken place, leading to the 

 production of a new character, or at least that a 

 germinal rearrangement has taken place, making 

 possible the appearance of the new^ character. If 

 it is not inherited, then the conclusion is that a 

 modification has been impressed on the organism 

 by some feature of the environment.* The question 

 to ask, then, is not whether heredity or environment 



* The possibility of the inheritance of acquired characters has 

 not been considered here, because if it ever occurs in mankind 

 it is probably too slow in its action to affect the practical problems 

 of eugenics. The subject has been discussed from an evolu- 

 tionary point of view elsewhere (Gates, 192 1, chap, viii.-xii.). 



