462 GENETICS IN RELATION TO AGRICULTURE 



but some characters seem to be too complex to admit readily of such form- 

 ulation. We may, therefore, justly draw the general conclusion that the 

 polyphyletic origin of modern breeds of farm animals has been a fruitful 

 source of germinal diversity. 



Mutation in Domestic Animals. The occurrence of mutations in higher 

 animals appears to be extremely rare, at least cases concerning which 

 definite evidence exists are very few. Those, however, which have 

 occurred appear to be strictly analogous in their nature and hereditary 

 behavior to the factor mutations in Drosophila; they involve changes in 

 definite loci in the germinal material. 



The Ancon sheep, one of the earliest authentic cases of the occurrence 

 of a mutation, has been discussed at some length by Darwin. This type 

 of sheep first appeared in a small flock kept by a Massachusetts farmer, 

 Seth Wright. The mutant, a ram lamb, was dropped in 1791. It had 

 an unusually long back, and short crooked legs, characters which appealed 

 to Farmer Wright, because sheep which possessed them could not readily 

 leap the fences which were so laboriously constructed at that time. 

 Seth Wright set to work, therefore, to establish a flock of Ancon sheep, 

 and he had no difficulty in doing so. Humphreys, commenting upon the 

 case, emphasizes the trueness with which the Ancon sheep bred to type, 

 there being only one doubtful case of a mating of an Ancon sheep and 

 ram which produced anything but Ancon offspring. In segregation the 

 character was always sharply discontinuous. The evidence that the 

 Ancon sheep arose by mutation is not unimpeachable, it might have 

 arisen by normal segregation of a recessive factor; but since no other case 

 of such segregation of the Ancon factor has been observed, the mutation 

 hypothesis appears best to account for it. The Ancon breed of sheep is 

 now extinct, having been displaced entirely by Merinos. 



Darwin discusses another case of a sport in sheep, namely that from 

 which the Mauchamp breed of France is derived. In this case a Merino 

 lamb which was dropped in 1828 had a fleece much superior to that of 

 the general flock; the wool was long and silky, and so desirable as to 

 command a price 25 per cent, greater than that of the best Merino wool. 

 By judicious use of this ram and subsequent rigorous selection M. Graux 

 was able to establish on Mauchamp farm a breed of sheep having all the 

 superior fleece qualities of this animal. 



But the case was not clear cut and definite like that of the Ancon 

 sheep. There was no evidence of distinct alternative inheritance, and 

 rigid selection was necessary in order to establish the new characters in a 

 pure race. In fact reexamination of the records in this case shows 

 clearly that the original ram lamb was not a mutant, but merely an 

 accidental hybrid from a ewe of the Mauchamp flock and a Dishley 

 ram of an adjoining flock. This case, therefore, as Nathusius points 



