OUR NATURAL INHERITANCE 63 



has often had to begin with a very small number of 

 similar forms. There has to be close inbreeding. If 

 fresh blood is introduced and offspring are born which 

 do not conform to the desired type, they are at once got 

 rid of. This elimination of divergent forms and this 

 inbreeding of similar forms may be continued for many 

 years until a large ' pure-bred ' herd is established. It 

 is marked by great uniformity and constancy of 

 character. As regards the features to which the breeder 

 has attended, each individual has what all the rest have, 

 none has what the others have not. Every one is as 

 good as his neighbour. They are pure-bred and they 

 breed true. If we could see into the invisible archi- 

 tecture of the germ-cells we should find that each had 

 the same equipment of similar ' factors ' or ' deter- 

 minants ' or * genes.' If two members of the herd are 

 paired, or if the members of two herds of similar history 

 are paired, the offspring are like the parents. Now, 

 among the various modes of inheritance this is one 

 extreme — strong hereditary resemblance, complete as 

 regards many characters, and appearing to the inex- 

 perienced eye complete through and through. 



(6) Another phenomenon, however, is the emergence 

 of something distinctively new. An offspring is born 

 that is in some respects very unlike its parents and its 

 kindred. It exhibits some novel pattern, some new 

 departure, a qualitative variation or mutation. In 

 manldnd this is illustrated by children with marked 

 originality, with great mathematical or musical ability, 

 or with less desirable idiosyncrasies. 



