Nature of Inherited Variations 213 



Actual hereditary changes in characters occur rather 

 rarely. This is apparently what is meant by the statement 

 that they appear suddenly ("sprungweise") ; for a time they 

 do not exist; then they do. (But the changes thus suddenly 

 occurring may be so minute as to be hardly detectible until 

 later changes in the same direction have accentuated them.) 



(3) Heritable changes may and often do occur in large 

 steps, so far as their effect on the developed characters of 

 adults is concerned. (This is an important fact; equally 

 important is the fact that heritable changes may be, and 

 often are, very minute.) 



(4) Appearances indicate that the changes are analogous 

 to (or actually are) chemical changes. When one chemical 

 compound changes into another, there is, it is held, no transi- 

 tional condition between the two, and the same is believed 

 to be true for hereditary variations. This conception of 

 the nature of hereditary variations accounts for the fact that 

 they often show in the adult as changes of large extent ; and 

 at the same time it fits equally well the minutely graded 

 hereditary changes that likewise occur. For there is no 

 change so minute that it may not be chemical in its nature. 

 In the immense organic molecule, with its thousands of 

 atoms, a shift of a single radical or single atom from one 

 position to another is a chemical change, though it may make 

 a difference so slight as to be almost beyond detection by 

 the most refined means. 



Whether a doctrine embodying these ideas differs from 

 that set forth by Darwin to such an extent as to deserve the 

 name of a new theory may be doubted. This will be a mat- 

 ter of individual opinion. 



The doctrine that hereditary changes must occur by large 

 steps evidently cannot be held. But what bearing on the 

 method of progressive evolution has the fact that they often 

 do occur by such steps, not by a series of gradual altera- 



