64 A MANUAL OF MENDELISM 



of the breed in the eighteenth century, has been most fully 

 investigated. Since the beginning of the nineteenth 

 century, Shorthorn breeders have disliked white and 

 preferred the other two colours, red and roan : sometimes 

 the one being in higher favour, sometimes the other. Thus 

 white has been much less frequently bred from ; yet whites 

 have not decidedly decreased, for the reason that they 

 are still thrown when roans are mated with each other. 

 Reds are thrown from the same matings, but, being not un- 

 welcome, their appearance occasions no remark. Breeders 

 have been aware that there were whites among the ancestry 

 of their breed, but, by breeding from reds and roans only, 

 have hoped to eliminate the " reversionary white " taint 

 and eventually have their roans breeding true. In this, 

 however, they have never succeeded. 



Before coming to the solution, it will be well to examine 

 the nature of the evidence upon which the problem is 

 solved. Because of their slow reproduction and therefore 

 of the time and expense which would be involved, experi- 

 ments with large animals are not readily undertaken. 

 We must have resort therefore to pedigree records in which 

 the results of all the possible matings are to be found — 

 in the present case to Coates's "Shorthorn Herd Book." 

 But such volumes are liable to errors which must be 

 identified and allowed for before the records can be used 

 as evidence. The chief errors in the " Shorthorn Herd 

 Book " arise from misdescriptions, non-registration of 

 calves of the imdesired colour, mistakenly attributed 

 paternity, and the substitution of a calf of a desired^for 

 another of the undesired colour. The last two errors may 

 be neglected generally and eliminated almost completely 

 by selecting data from the records of careful and reliable 

 breeders only. 



