200 COOK 



Supersexual dimorphism. 



Diversity in social organisms (politism). 

 Polar inheritance in crosses of narrow-bred varieties. 



Equipolar inheritance. 



Partial dominance. 



Complete dominance (mendelism). 



Interpolar inheritance. . f 



Mosaic inheritance. 



Extrapolar inheritance. 



Conjugate reversion. 



Perjugate reversion. 



Prepotent polarity. 

 Descent with averaging of differences (intermediate). 

 Descent with specific diversity (hybridism). 

 Sterile or mule hybrids (conjugate hybridism). 

 Fertile hybrids between species (perjugate hybridism). 



Unrestricted Descent with Normal Diversity i^Hetcrisni). — 

 Heterism is a method of descent in which the parent organisms 

 are members of an individually diverse, freely interbreeding 

 group, and the offspring reproduce the group diversit}^ instead 

 of being restricted to the expression of characters of the parent 

 individuals. Heterism is the most general condition or method 

 of descent, that found in widely distributed, broad-bred species 

 in nature. 



Reasons have been given in other places for believing that 

 organic evolution is a function of normal, specific networks of 

 descent — a process of change in a broad fabric of interbreed- 

 ing lines of descent.^ 



Inheritance, like descent, is a group phenomenon. Uni- 

 formity of inheritance is proportional to the uniformity of the 

 group to which the parent organisms belong. In broad-bfed 

 groups parent organisms are usually unlike. The offspring 

 are also unlike, and they do not merely reproduce the differ- 

 ences of the parents, but share the indiscriminate individual 

 diversity of the group. Even the simultaneous offspring of the 



'Cook, O. F., 1906. The Vital Fabric of Descent. Proc. Washington 

 Academy of Sciences, 7 : 301. Aspects of Kinetic Evolution. Proc. Washing- 

 ton Academy of Sciences, S: 197-403. 



