SCIENCE 



of so-called unit characters may depend, for 

 the most part, not upon germinal loss or gain, 

 but simply on transformation. Viewed in this 

 simple and natural way the appearance of a 

 new dominant character is not an event to be 

 marvelled at. Dominant and recessive charac- 

 ters not improbably owe their origin to much 

 the same causes. At least we do not know that 

 they do not. Concerning the real causes of 

 variations of any kind we know very little 

 more than we did when Darwin commented 

 on our profound ignorance of this subject. It 

 is therefore premature to pin our faith to any 

 particular theory of the origin of variation and 



especially to draw far-reaching conclusions re- 

 garding evolution on the basis of such an in- 

 terpretation. We may conceive variability as 

 due to germinal losses or gains for the sake of 

 our formulas, and there may be little harm in 

 so doing so long as it is clearly realized that 

 the procedure is a purely arbitrary and 

 schematic method of recording certain facts 

 of inheritance. But when we make the serious 

 attempt to apply the conception to what actu- 

 ally takes place in the germ plasm we en- 

 counter a fruitful source of fallacies. 



S. J. HOLMES 



UNIVERSITY OF CALIFORNIA 



