372 L. M. WINTERS 



er than the exception in the production of commercial corn. Wright (1922) 

 had several years previously published what has since turned out to be a 

 classic: The Report of the U.S.D.A. Studies of Inbreeding and Crossbreeding 

 with Guinea Pigs. Why then should the situation be different in livestock 

 than in corn and in guinea pigs? W^as it true that livestock failed to respond 

 to crossbreeding, and if so, why? A likely explanation appeared to be that our 

 breeds of livestock were not truly comparable to inbred lines of guinea pigs 

 and corn because they did not possess sufficient genetic purification. 



I am sorry now that I did not record in advance of this experiment the re- 

 sults that I expected to derive. Had I recorded them, they would have been 

 something like this: The crossing of the breeds of livestock will result in a 

 slight increase in vigor. The increase will be so slight that it is scarcely worth 

 while for the commercial producer, in contrast to the more simple procedure 

 of grading or the maintenance of a registered herd. Most of my severe critics 

 regarding crossbreeding will be quite surprised to read this statement. As 

 nearly as I can tell at this time, there were two major reasons for my belief. 

 The first was the accumulation of the continued absorption of a large amount 

 of teaching toward that end. The second was the general belief on the part 

 of geneticists that our breeds of farm animals had not been sufficiently puri- 

 fied nor separated genetically to yield hybrid vigor when crossed. 



If I had recorded all of my thoughts, they would have included this reser- 

 vation: If the crossing of the breeds does result in increased performance suf- 

 ficient to make crossing worth while, then the standard advice that had been 

 given through the years regarding the use of crossbred females for breeding 

 must be erroneous. This reservation was based on the results that Wright had 

 previously obtained in his use of crossbred guinea pigs as dams, and from the 

 information already available regarding the production of hybrid corn. At 

 this time there was no thought regarding continuous crossbreeding by either 

 rotation or crisscross breeding. The objectives were merely to find out if there 

 was any advantage in crossing the breeds for the market production of swine. 

 If there was an advantage in crossing the breeds for market production of 

 swine, was there then any advantage in retaining these crossbreds to become 

 future parents? 



In planning the experiment, provision was made whereby as nearly as 

 possible the same genetic material was put in the crosses as was produced 

 in the purebreds. In planning the use of crossbreds as parents, the original 

 plan called for the use of both crossbred females and crossbred males. My 

 senior officers informed me that they were willing to go along with me quite 

 a way in this crossbreeding study, but that when it came to the use of cross- 

 bred males, that was going just a bit too far and I would have to compromise. 

 I compromised on this point all too willingly. How I have wished, during the 

 last few years, that I had insisted on carrying out my original plan of 

 using both crossbred females and crossbred males in the experiment. But little 



