M Database Inspector (cheetah)
Not logged in. Login


54 rows, page 1 of 14 (4/p)
1 2 3 4 5 6 7 8 9 10 11 12 13 14

Export to Excel select * from OriginOfSpecies where subject = '01 - Variations Under Domestication' order by description limit 4 (Page 1: Row)
subject
title
ordinal
description Desending Order (top row is first)
01 - Variations Under Domestication 01-11 - Unknown Origin of our Domestic Productions 10 A large amount of change, thus slowly and unconsciously accumulated, explains, as I believe, the well-known fact, that in a number of cases we cannot recognise, and therefore do not know, the wild parent-stocks of the plants which have been longest cultivated in our flower and kitchen gardens.

If it has taken centuries or thousands of years to improve or modify most of our plants up to their present standard of usefulness to man, we can understand how it is that neither Australia, the Cape of Good Hope, nor any other region inhabited by quite uncivilised man, has afforded us a single plant worth culture.

It is not that these countries, so rich in species, do not by a strange chance possess the aboriginal stocks of any useful plants, but that the native plants have not been improved by continued selection up to a standard of perfection comparable with that acquired by the plants in countries anciently civilised.

Australia
Australia

Cape of Good Hope
Cape of Good Hope
01 - Variations Under Domestication 01-08 - Breeds of the Domestic Pigeons, their Differences and Origin 30 Altogether at least a score of pigeons might be chosen, which, if shown to an ornithologist, and he were told that they were wild birds, would certainly be ranked by him as well-defined species.

Moreover, I do not believe that any ornithologist would in this case place the English carrier, the short-faced tumbler, the runt, the barb, pouter, and fantail in the same genus; more especially as in each of these breeds several truly-inherited sub-breeds, or species, as he would call them, could be shown him.

English Carrier Pigeon
English Carrier Pigeon

Short Faced Tumbler Pigeon
Short Faced Tumbler Pigeon

Runt Pigeon
Runt Pigeon

Barb Pigeon
Barb Pigeon

Pouter Pigeon
Pouter Pigeon

Fantail Pigeon
Fantail Pigeon
01 - Variations Under Domestication 01-04 - Inheritance 20 Any variation which is not inherited is unimportant for us.

But the number and diversity of inheritable deviations of structure, both those of slight and those of considerable physiological importance, are endless. Dr. Prosper Lucas's treatise, in two large volumes, is the fullest and the best on this subject.

No breeder doubts how strong is the tendency to inheritance; that like produces like is his fundamental belief: doubts have been thrown on this principle only by theoretical writers.

When any deviation of structure often appears, and we see it in the father and child, we cannot tell whether it may not be due to the same cause having acted on both; but when amongst individuals, apparently exposed to the same conditions, any very rare deviation, due to some extraordinary combination of circumstances, appears in the parent- say, once amongst several million individuals- and it reappears in the child, the mere doctrine of chances almost compels us to attribute its reappearance to inheritance.

Every one must have heard of cases of albinism, prickly skin, hairy bodies, &c., appearing in several members of the same family.

If strange and rare deviations of structure are really inherited, less strange and commoner deviations may be freely admitted to be inheritable.

Perhaps the correct way of viewing the whole subject would be, to look at the inheritance of every character whatever as the rule, and non-inheritance as the anomaly?
Full Size
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