THE FOUNTAIN OF CHANGE 243 



to reach certainty in regard to this simple point, 

 but there is no harm in asking, as Dr. Gates does, 

 whether the white man may have originated from a 

 black race by a " tetraploid mutation and its conse- 

 quences." The nuclear change need not, of course, 

 affect the number of the chromosomes ; it may 

 affect shape and size and structure. More funda- 

 mentally but no longer visibly a chromosome 

 may undergo a change in its stereochemic archi- 

 tecture or in its functional powers. We know of 

 remarkable mutations in bacteria, which some- 

 times change suddenly in their physiological prop- 

 erties. 



The mutation theory is concerned with the origin 

 of new characters, and Mendelism is concerned with 

 their behavior in inheritance; so the two theories 

 touch, and it is interesting to notice Dr. Gates' 

 position. In the first place, it seems clear that there 

 is no warrant for supposing that (Enothcra lamarcki- 

 ana has had a mixed ancestry and that its mutabil- 

 ity (still unexhausted) is a result of this. Mutations 

 may occur apart altogether from crossing, though 

 crossing may increase their frequency or even 

 initiate a condition of germinal instability. In the 

 second place, the Mendelian classification of all new 

 characters into dominants (due to the addition of a 

 factor) and rccessives (due to the loss of a factor) 

 is much too hard and fast to cover all the facts. 

 Germinal changes are of many and diverse kinds, 

 and are not exhausted by addition or loss of unit 

 factors. Some mutations illustrate Mendelian 



