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 reéxamination 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 
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