No. 592] SHORTER ARTICLES AND DISCUSSION 255 



tion guided by rational selection in a particular direction that 

 has made possible the doubling in size that most of our domesti- 

 cated animals have undergone since they were taken from the 

 wild state? And does any one seriously think that a single selec- 

 tion from wild stock has produced for us the enormous horses of 

 Flanders, or the little ponies of the Shetland Isles, the enormous 

 sheep of the Scotch highlands, or the huge rabbits of Europe, 

 each a monstrosity in comparison with its most probable wild 

 ancestors, and yet producing blends in crosses with them? This 

 blending shows that the change has been one of slow accomplish- 

 ment and not the result of sudden discontinuous change. 



When we compare the color varieties of domestic animals with 

 those of their wild ancestors, as I have been able personally to 

 do in the case of cavies, we are struck by the fact that the domes- 

 tic varieties are relatively clear and distinct in color, either more 

 intense, more dilute, or of purer color than we can obtain from 

 the wild form by simple recombination of genetic factors. For 

 example it is possible by crosses to obtain from wild cavies the 

 retrogressive varieties, black and yellow. But such synthetic 

 blacks lack the full intensity of blackness found in our best 

 strains of black guinea-pigs, and the synthetic yellows are apt to 

 be either pale or muddy in yellowness, lacking the intensity and 

 brilliancy of our best domestic varieties. It is impossible to 

 escape the impression that our improved domestic varieties are 

 not mere factorial recombinations derived from wild species, but 

 that they have been forced up to a higher standard by repeated 

 selection ; that the breeder, for example, has first observed vari- 

 ation in intensity of blackness among his blacks (doubtless ob- 

 tained originally from a retrogressive sport) and that by re- 

 peatedly selecting the blackest available individuals he has in- 

 creased the blackness of the race. Thus it is no accident that 

 the meat and milk and wool producing capacity of our domes- 

 tic animals far exceeds that of any wild ancestral species. The 

 standard in each case has been raised and it has not been raised 

 by a single lucky accident (the mutation view), but by a series of 

 slow advances each impossible until a previous advance had been 

 made. I am aware indeed that Pearl at one time maintained an 

 opposite view, holding (if I remember correctly) that our best 

 strains of poultrv are no better layers than some strains of jungle 

 fowl. But I do not believe that this view can be successfully de- 

 fended. I am certain that such an idea is quite preposterous in 



