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01 - Variations Under Domestication 01-07 - Origin of Domestic Varieties from one or more Species 70 It has often been loosely said that all our races of dogs have been produced by the crossing of a few aboriginal species; but by crossing we can only get forms in some degree intermediate between their parents; and if we account for our several domestic races by this process, we must admit the former existence of the most extreme forms, as the Italian greyhound, bloodhound, bulldog, &c., in the wild state.

greyhound
greyhound

bloodhound
bloodhound


Moreover, the possibility of making distinct races by crossing has been greatly exaggerated. Many cases are on record, showing that a race may be modified by occasional crosses, if aided by the careful selection of the individuals which present the desired character; but to obtain a race intermediate between two quite distinct races, would be very difficult. Sir J. Sebright expressly experimented with this object and failed.

The offspring from the first cross between two pure breeds is tolerably and sometimes (as I have found with pigeons) quite uniform in character, and everything seems simple enough; but when these mongrels are crossed one with another for several generations, hardly two of them are alike and then the difficulty of the task becomes manifest.

pigeon
pigeon
01 - Variations Under Domestication 01-05 -Character of Domestic Varieties 10 When we look to the hereditary varieties or races of our domestic animals and plants, and compare them with closely allied species, we generally perceive in each domestic race, as already remarked, less uniformity of character than in true species.
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Domestic races often have a somewhat monstrous character; by which I mean, that, although differing from each other, and from other species of the same genus, in several trifling respects, they often differ in an extreme degree in some one part, both when compared one with another, and more especially when compared with the species under nature to which they are nearest allied. With these exceptions (and with that of the perfect fertility of varieties when crossed,- a subject hereafter to be discussed), domestic races of the same species differ from each other in the same manner as do the closely-allied species of the same genus in a state of nature, but the differences in most cases are less in degree.

This must be admitted as true, for the domestic races of many animals and plants have been ranked by some competent judges as the descendants of aboriginally distinct species, and by other competent judges as mere varieties.
01 - Variations Under Domestication 01-04 - Inheritance 40 Having alluded to the subject of reversion, I may here refer to a statement often made by naturalists- namely, that our domestic varieties, when run wild, gradually but invariably revert in character to their aboriginal stocks.

Hence it has been argued that no deductions can be drawn from domestic races to species in a state of nature.

I have in vain endeavoured to discover on what decisive facts the above statement has so often and so boldly been made.

There would be great difficulty in proving its truth: we may safely conclude that very many of the most strongly marked domestic varieties could not possibly live in a wild state.

In many cases, we do not know what the aboriginal stock was, and so could not tell whether or not nearly perfect reversion had ensued. It would be necessary, in order to prevent the effects of intercrossing, that only a single variety should have been turned loose in its new home.

Nevertheless, as our varieties certainly do occasionally revert in some of their characters to ancestral forms, it seems to me not improbable that if we could succeed in naturalising, or were to cultivate, during many generations, the several races, for instance, of the cabbage, in very poor soil (in which case, however, some effect would have to be attributed to the definite action of the poor soil), that they would, to a large extent, or even wholly,
revert to the wild aboriginal stock.

cabbage
cabbage
.

Whether or not the experiment would succeed, is not of great importance for our line of argument; for by the experiment itself the conditions of life are changed.

Heisenberg
Heisenberg
.

If it could be shown that our domestic varieties manifested a strong tendency to reversion,- that is, to lose their acquired characters, whilst kept under the same conditions, and whilst kept in a considerable body, so that free intercrossing might check, by blending together, any slight deviations in their structure, in such case, I grant that we could deduce nothing from domestic varieties
in regard to species. But there is not a shadow of evidence in favour of this view: to assert that we could not breed our cart- and race-horses, long and short-horned cattle, and poultry of various breeds, and esculent vegetables, for an unlimited number of generations, would be opposed to all experience.
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horses
horses

cow
cow

fowl
fowl
01 - Variations Under Domestication 01-06 - Difficulty of distinguishing between Varieties and Species 10 In attempting to estimate the amount of structural differencebetween allied domestic races, we are soon involved in doubt, from not knowing whether they are descended from one or several parent species.

This point, if it could be cleared up, would be interesting; if, for instance, it could be shown that the greyhound, bloodhound, terrier, spaniel, and bull-dog, which we all know propagate their kind truly, were the offspring of any single species, then such facts would have great weight in making us doubt about the immutability of the many closely allied natural species-

greyhound
greyhound

bloodhound
bloodhound

terrier
terrier

spaniel
spaniel

bulldog
bulldog


for instance, of the many foxes- inhabiting different quarters of the world. I do not believe, as we shall presently see, that the whole amount of difference between the several breeds of the dog has been produced under domestication;

fox
fox


I believe that a small part of the difference is due to their being descended from distinct species.

In the case of strongly marked races of some other domesticated species, there is presumptive or even strong evidence, that all are descended from a single wild stock.