01 - Variations Under Domestication

01-12 - Circumstances favourable to Man's Power of Selection

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

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

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.

01 - Variations Under Domestication

01-12 - Circumstances favourable to Man's Power of Selection

But the goose, under the conditions to which it is exposed when domesticated seems to have a singularly inflexible organisation, though it has varied to a slight extent, as I have elsewhere described.

goose

Some authors have maintained that the amount of variation in our domestic productions is soon reached, and can never afterwards be exceeded.

It would be somewhat rash to assert that the limit has been attained in any one case; for almost all our animals and plants have been greatly improved in many ways within a recent period; and this implies variation.

It would be equally rash to assert that characters now increased to their utmost limit, could not, after remaining fixed for many centuries, again vary under new conditions of life.

No doubt, as Mr. Wallace has remarked with much truth, a limit will be at last reached. For instance, there must be a limit to the fleetness of any terrestrial animal, as this will be determined by the friction to be overcome, the weight of body to be carried, and the power of contraction in the muscular
fibres.

Alfred Russel Wallace

But what concerns us is that the domestic varieties of the same species differ from each other in almost every character, which man has attended to and selected, more than do the distinct species of the same genera.

Isidore Geoffroy St-Hilaire has proved this in regard to size, and so it is with colour and probably with the length of hair.

With respect to fleetness, which depends on many bodily characters, Eclipse was far fleeter, and a dray-horse is incomparably stronger than any two natural species belonging to the same genus.

So with plants, the seeds of the different varieties of the bean or maize probably differ more in size, than do the seeds of the distinct species in any one genus in the same two families. The same remark holds good in regard to the fruit of the several varieties of the plum, and still more strongly with the melon, as well as in many other analogous cases.

maize

plum

melon