376 EXPERIMENTAL STUDY OF INHERITANCE 



enormously enhances the importance of the hereditary factor 

 in determining evolution; for it leads us to realise more 

 strongly the power of persistence that definite characters may 

 have even when there is intercrossing. Definite characters for 

 good or ill, whether dominant or recessive, do not disappear 

 in Mendelian inheritance. They persistently reappear in their 

 original " purity." 



Thus, Mr. Punnett writes : " Permanent progress is a question 

 of breeding rather than of pedagogics ; a matter of gametes, not 

 of training. As our knowledge of heredity clears and the mists 

 of superstition are dispelled, there grows upon us with an ever- 

 increasing and relentless force the conviction that the creature 

 is not made, but born " (1905, p. 60). 



Inbreeding. — Breeders who have with carefulness evolved a 

 fine herd are often very loath to introduce fresh blood, even when 

 they suspect that they are approaching the limits of safe in- 

 breeding. But ij Mendelism applies to the organisms bred, 

 then it does not seem as if the introduction of fresh blood need 

 affect the purity of the stock. A cross is effected with a view to 

 secure reinvigoration ; the results of the cross may be inbred, 

 and ij Mendelism applies, then forms like the original parent will 

 reappear in the next generation, and the forms not wanted can 

 be disposed of. Let us put it once more in schematic form : 



Old-established form. " Fresh blood." 

 A B 



If A be dominant, A(B) ; or B(A), if B be dominant. 



X X 



A A 



« A + w A(B) nK + n B(A) 



Or if A(B) be inbred the result will be w A + 2 w A(B) + m B. 

 Or if B(A) be inbred the result will be m A + 2 w B(A) + « B. 

 There is obviously no theoretical danger of losing A. 



