476 TRANSMISSION 



" tastes." This being true, we are often disappointed in trying 

 to modify or tone down a vicious disposition by mating with 

 one of milder temper, the progeny tending to follow the average 

 of the race, or else to be as vicious as the objectionable parent. 



Particulate inheritance, inheritance by type, or bit by bit. 

 Characters are often so closely associated (correlated) as to 

 move in company, so that whole groups of characters appear 

 and disappear together, even when there is little or no known 

 causative relation between them. Whether this is merely acci- 

 dental association of characters not mutually exclusive, and certain 

 to happen occasionally under the law of chance, or whether it 

 is due, rather, to some deeper-lying principle, is perhaps uncer- 

 tain ; but it is surely true that man, for example, runs in types, 

 and whoever has traveled much, or has enjoyed a fairly exten- 

 sive acquaintance, has met many people of no blood relationship, 

 in places widely separated, who yet were clearly of the same 

 type, and whose similarity became more evident upon closer 

 acquaintance. 1 



Clearly, characters are not altogether independent one of 

 another, and often the greatest difficulty is encountered in 

 breaking up a group, some members of which are desirable and 

 others objectionable. So inheritance is often " bit by bit," as if 

 the unit of transmission were larger and more complex than the 

 single character ; as if a kind of permanent partnership were in 

 force. The biological basis of all this, if it really exists, will 

 probably remain for a long time hidden, but coefficients of 

 correlation afford at least a method for determining the degree 

 and the persistence of this copartnership. 



Polymorphism and sexual dimorphism. Many races, instead 

 of showing all intermediate gradations from one extreme to the 

 other, in respect to size for example, or color, or any other 

 character or association of characters, will exhibit two, three, 

 or more forms or types, so different and distinct as often to be 



1 In practical breeding operations the greatest need exists for exact knowledge 

 of correlated characters. The methods given in the preceding chapter enable the 

 student to determine quantitatively the real extent of correlation, and breeders 

 should prosecute most industriously the study of this subject, until they are well 

 informed as to the real relations of all valuable characters of domesticated 

 animals and plants. 



