loo PROBLEMS OF EVOLUTION 



certainly have been checked by artificial selection, and the ex- 

 tremities of the wing, both the bones and the feathers, have no 

 doubt been preserved by correlation. We may fairly argue, 

 however, that if a slackening of selection can produce some 

 decline from a high standard, then a total cessation would pro- 

 duce much greater results. If domestic ducks are comparatively 

 imbecile, it is due to a partial application of pammixis. The un- 

 restricted working of it, therefore, would be likely to produce 

 complete idiocy. The same argument would hold with regard 

 to the health of domesticated breeds. There is reason to believe 

 their health has to some extent deteriorated. Certainly domesti- 

 cated pigeons suffer from a variety of diseases. Horses no less. 

 High breeding and delicacy of health are often found to go 

 together. And yet the breeder does not disregard the question 

 of health, he only considers it as secondary. So that here too 

 there is decreased stringency of selection, producing appreciable 

 results. 



We look in vain among domestic breeds for a case in which 

 pammixis has had free play. If an organ has no use in the 

 artificial environment, the breeder has either protected it (if 

 correlation left it undefended) or has hastened its disappearance 

 by selection. The most instructive fact is, I think, the ease 

 with which hornless breeds of cattle and sheep and goats have 

 been formed. The horns of milch cows show the variability 

 that absence of selection causes. Where there is instability, 

 Sudden there are likely to be instances of sudden and complete disappearance 

 eteToss f ^ e or S an - Now, the hornless breeds have been formed by 

 selection of such monstrosities. 1 In the absence of selection no 

 doubt intercrossing would have made the results less startling. 

 But it is probable a race having horns of very variable (usually 

 small) dimensions might have arisen independently of selection 

 and within a comparatively short space of time. In the course of 

 a score or two of generations the organ might have come to be 

 normally a mere vestige. 



1 Dr E. A. Saunders has recently told me of an Aylesbury duck seen by him, 

 between the toes of which there was absolutely no webbing. Apparently in this 

 case there was no variability in the breed preceding the complete loss in this 

 individual 



