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01 - Variations Under Domestication 01-03 - correlation of Growth 10 Many laws regulate variation, some few of which can be dimly seen, and will hereafter be briefly discussed.

I will here only allude to what may be called correlated variation. Important changes in the embryo or larva will probably entail changes in the mature animal.

In monstrosities, the correlations between quite distinct parts are very curious; and many instances are given in Isidore Geoffroy St-Hilaire's great work on this subject.
Isidore Geoffroy Saint Hilaire
Isidore Geoffroy Saint Hilaire


Breeders believe that long limbs are almost always accompanied by an elongated head.

Some instances of correlation are quite whimsical: thus cats which are entirely white and have blue eyes are generally deaf;

but it has been lately stated by Mr. Tait that this is confined to the males.

Colour and constitutional peculiarities go together, of which many remarkable cases could be given amongst animals and plants.
From facts collected by Heusinger, it appears that white sheep and pigs are injured by certain plants, whilst dark-coloured individuals escape:

sheep
sheep

pig
pig
01 - Variations Under Domestication 01-09 - Principles of Selection anciently followed, and their Effects 10 Let us now briefly consider the steps by which domestic races have been produced, either from one or from several allied species.

Some effect may be attributed to the direct and definite action of the external conditions of life, and some to habit; but he would be a bold man who would account by such agencies for the differences between a dray- and race-horse, a greyhound and bloodhound, a carrier and tumbler pigeon.

Dray Horse
Dray Horse

Race Horse
Race Horse

greyhound
greyhound

bloodhound
bloodhound

Tumbler Pigeon
Tumbler Pigeon


One of the most remarkable features in our domesticated races is that we see in them adaptation, not indeed to the animal's or plant's own good, but to man's use or fancy.

Some variations useful to him have probably arisen suddenly, or by one step; many botanists, for instance, believe that the fuller's teasel, with its hooks, which cannot be rivalled by any mechanical contrivance, is only a variety of the wild Dipsacus; and this amount of change may have suddenly arisen in a seedling.

Fuller's Teasel
Fuller's Teasel


So it has probably been with the turnspit dog; and this is known to have been the case with the ancon sheep.

But when we compare the dray-horse and race-horse, the dromedary and camel, the various breeds of sheep fitted either for cultivated land or mountain pasture, with the wool of one breed good for one purpose, and that of another breed for another purpose; when we compare the many breeds of dogs, each good for man in different ways; when we compare the game-cock, so pertinacious in battle, with other breeds so little quarrelsome, with "everlasting layers" which never desire to sit, and with the bantam so small and elegant; when we compare the host of agricultural, culinary, orchard, and flower-garden races of plants, most useful to man at different seasons and for different purposes, or so beautiful in his eyes, we must, I think, look further than to mere variability.

Ancon Sheep
Ancon Sheep

Dray Horse
Dray Horse

Race Horse
Race Horse

camel
camel

sheep
sheep


We cannot suppose that all the breeds were suddenly produced as perfect and as useful as we now see them; indeed, in many cases, we know that this has not been their history. The key is man's power of accumulative selection: nature gives successive variations; man adds them up in certain directions useful to him. In this sense he may be said to have made for himself useful breeds.
01 - Variations Under Domestication 01-07 - Origin of Domestic Varieties from one or more Species 10 In the case of most of our anciently domesticated animals and plants, it is not possible to come to any definite conclusion, whether they are descended from one or several wild species.

The argument mainly relied on by those who believe in the multiple origin of our domestic animals is, that we find in the most ancient times, on the monuments of Egypt, and in the lake-habitations of Switzerland, much diversity in the breeds;

Egypt
Egypt

Switzerland
Switzerland



and that some of these ancient breeds closely resemble, or are even identical with, those still existing.

But this only throws far backwards the history of civilisation, and shows that animals were domesticated at a much earlier period than has hitherto been supposed.
01 - Variations Under Domestication 01-12 - Circumstances favourable to Man's Power of Selection 10 I will now say a few words on the circumstances, favourable, or the reverse, to man's power of selection.

A high degree of variability is obviously favourable, as freely giving the materials for selection to work on; not that mere individual differences are not amply sufficient, with extreme care, to allow of the accumulation of a large amount of modification in almost any desired direction.

But as variations manifestly useful or pleasing to man appear only occasionally, the chance of their appearance will be much increased by a large number of individuals being kept Hence, number is of the highest importance for success.

On this principle Marshall formerly remarked, with respect to the sheep of parts of Yorkshire, "as they generally belong to poor people, and are mostly in small lots, they never can be improved." On the other hand, nurserymen, from keeping large stocks of the same plant, are generally far more successful than amateurs in raising new and valuable varieties.

sheep
sheep

seedling
seedling


A large number of individuals of an animal or plant can be reared only where the conditions for its propagation are favourable. When the individuals are scanty, all will be allowed to breed, whatever their quality may be, and this will effectually prevent selection.

But probably the most important element is that the animal or plant should be so highly valued by man, that the closest attention is paid to even the slightest deviations in its qualities or structure.

Unless such attention be paid nothing can be effected.

I have seen it gravely remarked, that it was most fortunate that the strawberry began to vary just when gardeners began to attend to this plant.

strawberry
strawberry


No doubt the strawberry had always varied since it was cultivated, but the slightest varieties had been neglected.

As soon, however, as gardeners picked out individual plants with slightly larger, earlier, or better fruit, and raised seedlings from them, and again picked out the best seedlings and bred from them, then (with some aid by crossing distinct species) those many admirable varieties of the strawberry were raised which have appeared during the last half-century.