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01 - Variations Under Domestication 01-01 - Causes of Variability 30 I may add, that as some organisms breed freely under the most unnatural conditions (for instance, rabbits and ferrets kept in hutches), showing that their reproductive organs are not easily affected;

rabbit
rabbit

ferret
ferret


so will some animals and plants withstand domestication or cultivation, and vary very slightly- perhaps hardly more than in a state of nature. Some naturalists have maintained that all variations are connected with the act of sexual reproduction;

but this is certainly an error; for I have given in another work a long list of "sporting plants," as they are called by gardeners;- that is, of plants which have suddenly produced a single bud with a new and sometimes widely different character from that of the other buds on the same plant.

These bud variations, as they may be named, can be propagated by grafts, offsets, &c., and sometimes by seed.

graft
graft


They occur rarely under nature, but are far from rare under culture.

As a single bud out of the many thousands, produced year after year on the same tree under uniform conditions, has been known suddenly to assume a new character; and as buds on distinct trees, growing under different conditions, have sometimes yielded nearly the same variety- for instance, buds on peach-trees producing nectarines, and buds on common roses producing moss-roses- we clearly see that the nature of the conditions is of subordinate importance in comparison with the nature of the organism in determining each particular form of variation;-
bud
bud

tree
tree

peach
peach

nectarine
nectarine

rose
rose

Moss Rose
Moss Rose


perhaps of not more importance than the nature of the spark, by which a mass of combustible matter is ignited, has in determining the nature of the flames.
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01 - Variations Under Domestication 01-01 - Causes of Variability 10 WHEN we compare the individuals of the same variety or sub-variety of our older cultivated plants and animals, one of the first points which strikes us is, that they generally differ more from each other than do the individuals of any one species or variety in a state of nature.
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And if we reflect on the vast diversity of the plants and animals which have been cultivated, and which have varied during all ages under the most different climates and treatment, we are driven to conclude that this great variability is due to our domestic productions having been raised under conditions of life not so uniform as, and somewhat different from, those to which the parent species had been exposed under nature.

There is, also, some probability in the view propounded by Andrew Knight, that this variability may be partly connected with excess of food.
Thomas Andrew Knight
Thomas Andrew Knight


It seems clear that organic beings must be exposed during several generations to new conditions to cause any great amount of variation; and that, when the organization has once begun to vary, it generally continues varying for many generations.

No case is on record of a variable organism ceasing to vary under cultivation.

Our oldest cultivated plants, such as wheat, still yield new varieties: our oldest, domesticated animals are still capable of rapid improvement or modification.

durum
durum

Angus
Angus
01 - Variations Under Domestication 01-01 - Causes of Variability 20 As far as I am able to judge, after long attending to the subject, the conditions of life appear to act in two ways,- directly on the whole organization or on certain parts alone, and indirectly by affecting the reproductive system.

With respect to the direct action, we must bear in mind that in every case, as Professor Weismann has lately insisted, and as I have incidentally shown in my work on Variation under Domestication, there are two factors: namely, the nature of the organism, and the nature of the conditions.

August Weismann
August Weismann


The former seems to be much the more important; for nearly similar variations sometimes arise under, as far as we can judge, dissimilar conditions; and, on the other hand, dissimilar variations arise under conditions which appear to be nearly uniform.

The effects on the offspring are either definite or indefinite.

They may be considered as definite when all or nearly all the offspring of individuals exposed to certain conditions during several generations are modified in the same manner.

It is extremely difficult to come to any conclusion in regard to the extent of the changes which have been thus definitely induced.

There can, however, be little doubt about many slight changes,- such as size from the amount of food, colour from the nature of the food, thickness of the skin and hair from climate, &c.

Each of the endless variations which we see in the plumage of our fowls must have had some efficient cause; and if the same cause were to act uniformly during a long series of generations on. many individuals, all probably would be modified in the same manner.

fowl
fowl


Such facts as the complex and extraordinary out-growths which variably follow from the insertion of a minute drop of poison by a gall-producing insect, show us what singular modifications might result in the case of plants from a chemical change in the nature of the sap. Indefinite variability is a much more common result of changed conditions than definite variability, and has probably played a more important part in the formation of our domestic races.

sap
sap
01 - Variations Under Domestication 01-01 - Causes of Variability 22 We see indefinite variability in the endless slight peculiarities which distinguish the individuals of the same species, and which cannot be accounted for by inheritance from either parent or from some more remote ancestor.

Even strongly marked differences occasionally appear in the young of the same litter, and in seedlings from the same seed-capsule.

litter
litter

seedling
seedling


At long intervals of time, out of millions of individuals reared in the same country and fed on nearly the same food, deviations of structure so strongly pronounced as to deserve to be called monstrosities arise; but monstrosities cannot be separated by any distinct line from slighter variations.
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All such changes of structure, whether extremely slight or strongly marked, which appear amongst many individuals living together, may be considered as the indefinite effects of the conditions of life on each individual organism, in nearly the same manner as the chill affects different men in an indefinite manner, according to their state of body or constitution, causing coughs or colds, rheumatism,
or inflammation of various organs.
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