354 THE AMEBIC AN NATURALIST [Vol. XL VI 



that the horn character may vary, they assure us that 

 this condition is due to a different unit and is not deriv- 

 able from the other, and they challenge us to produce it 

 from the other. If we begin measuring the horns of our 

 cattle and picking out those a little shorter than the 

 average, we find that offspring are obtained witli horns 

 of practically average length. Perhaps we repeat the 

 selection half-a-dozen times and begin to get a barely 

 appreciable result. They interrupt, "See here," they 

 say, "you're not getting anywhere; give up and acknowl- 

 edge yourself beaten. If you stop your selecting for a 

 single generation, the little you have accomplished will 

 disappear. See meantime what we mutationists have ac- 

 complished; we have dehorned half-a-dozen breeds by 

 simple crossing. This is more than you could do in a 

 thousand years." Such comment on our work is ex- 

 tremely disquieting, for our progress is slow, and we can 

 only reply, "Your method is the quicker one to get rid 

 of a character altogether, but you admit yourself power- 

 less to create a condition which you do not possess fully 

 realized at the outset. We do not admit ourselves so 

 helpless ; we hope to get something which we do not now 

 have, and we are willing to wait a while for it. We be- 

 lieve that we can create what does not now exist. This 

 you confess yourself powerless to do." 



The foregoing states fairly, I think, the present views 

 regarding selection as a tool of the breeder held on one 

 hand by the mutationists and pure-line advocates, and 

 on the other hand by a minority of Mendelians who like 

 myself consider selection an important creative agency 

 in breeding. 



The fundamental point of difference between these two 

 views lies in their different conception of unit-characters. 

 To the mutationist unit-characters are as changeless as 

 atoms and as uniform as the capacity of a quart meas- 

 ure. Theoretically an atom is an atom under all circum- 

 stances, and a quart holds the same anywhere and every- 

 where. But the worldly-wise know that the actual quart 

 is not the same in all places ; it is apt to be smaller at the 



