The Variation of Animals and Plants under Domestication, vol 2 | Page 9

to have played false with one
of the greyhounds, and the whole litter was condemned; but the
gamekeeper was permitted to save one as a curiosity. Two years
afterwards a friend of the owner saw the young dog, and declared that

he was the image of his old pointer-bitch Sappho, the only blue and
white pointer of pure descent which he had ever seen. This led to close
inquiry, and it was proved that he was the great-great-grandson of
Sappho; so that, according to the common expression, he had only
1/16th of her blood in his veins. I may give one other instance, on the
authority of Mr. R. Walker, a large cattle- breeder in Kincardineshire.
He bought a black bull, the son of a black cow with white legs, white
belly and part of the tail white; and in 1870 a calf the
gr.-gr.-gr.-gr.-grandchild of this cow was born coloured in the same
very peculiar manner; all the intermediate offspring having been black.
In these cases there can hardly be a doubt that a character derived from
a cross with an individual of the same variety reappeared after passing
over three generations in the one case, and five in the other.
When two distinct races are crossed, it is notorious that the tendency in
the offspring to revert to one or both parent-forms is strong, and
endures for many generations. I have myself seen the clearest evidence
of this in crossed pigeons and with various plants. Mr. Sidney (13/17.
In his edition of 'Youatt on the Pig' 1860 page 27.) states that, in a litter
of Essex pigs, two young ones appeared which were the image of the
Berkshire boar that had been used twenty-eight years before in giving
size and constitution to the breed. I observed in the farmyard at Betley
Hall some fowls showing a strong likeness to the Malay breed, and was
told by Mr. Tollet that he had forty years before crossed his birds with
Malays; and that, though he had at first attempted to get rid of this
strain, he had subsequently given up the attempt in despair, as the
Malay character would reappear.
This strong tendency in crossed breeds to revert has given rise to
endless discussions in how many generations after a single cross, either
with a distinct breed or merely with an inferior animal, the breed may
be considered as pure, and free from all danger of reversion. No one
supposes that less than three generations suffices, and most breeders
think that six, seven, or eight are necessary, and some go to still greater
lengths. (13/18. Dr. P. Lucas, 'Hered. Nat.' tome 2 pages 314, 892: see a
good practical article on the subject in 'Gardener's Chronicle' 1856 page
620. I could add a vast number of references, but they would be

superfluous.) But neither in the case of a breed which has been
contaminated by a single cross, nor when, in the attempt to form an
intermediate breed, half-bred animals have been matched together
during many generations, can any rule be laid down how soon the
tendency to reversion will be obliterated. It depends on the difference
in the strength or prepotency of transmission in the two parent-forms,
on their actual amount of difference, and on the nature of the conditions
of life to which the crossed offspring are exposed. But we must be
careful not to confound these cases of reversion to characters which
were gained by a cross, with those under the first class, in which
characters originally common to BOTH parents, but lost at some
former period, reappear; for such characters may recur after an almost
indefinite number of generations.
The law of reversion is as powerful with hybrids, when they are
sufficiently fertile to breed together, or when they are repeatedly
crossed with either pure parent-form, as in the case of mongrels. It is
not necessary to give instances. With plants almost every one who has
worked on this subject, from the time of Kolreuter to the present day,
has insisted on this tendency. Gartner has recorded some good
instances; but no one has given more striking ones than Naudin. (13/19.
Kolreuter gives curious cases in his 'Dritte Fortsetzung' 1766 ss. 53, 59;
and in his well-known 'Memoirs on Lavatera and Jalapa.' Gartner
'Bastarderzeugung' ss. 437, 441, etc. Naudin in his "Recherches sur
l'Hybridite" 'Nouvelles Archives du Museum' tome 1 page 25.) The
tendency differs in degree or strength in different groups, and partly
depends, as we shall presently see, on whether the parent-plants have
been long cultivated. Although the tendency to reversion is extremely
general with nearly all mongrels and hybrids, it cannot be considered as
invariably characteristic of them; it may also be mastered by
long-continued selection; but these subjects will more properly be
discussed in