I2O Heredity and Social Progress 



a swift one. Rapid shiftings of large amounts 

 are made by subtraction in every process 

 where equilibrium is preserved. Vital pro- 

 cesses also depend on this principle. Growth 

 alternates between two parts, while the de- 

 struction, which disturbs the equilibrium on 

 which growth depends, is limited to one part. 

 Devolution must, therefore, operate as the 

 subtracting force upon related parts until an 

 equilibrium is formed. Then growth asserts 

 itself and life is revived. 



The agent of devolution is emotion. Ad- 

 verse conditions, the source of emotions, cause 

 a shock or a nervous explosion which follows, 

 not the bilateral paths of structure, but the 

 most direct routes for its dispersion. If this 

 leaves the organism in an unbalanced condi- 

 tion, devolution must create an equality by cut- 

 ting back the unaffected parts until growth can 

 assume its normal course. Emotions always 

 arise where there is a lack of balance between 

 two related parts, and disruptive activity con- 

 tinues until despecialization and simplification 

 restore the equilibrium. Unbalanced kata- 

 bolic processes destroy until the restored 



