Origin of Species Variorum

↑ 13 blocks not present in 1859 1860 1861 1866; present in 1869 1872

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 organisation 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. 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 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. Such facts as the complex and extraordinary out-growths which invariably 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. 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-capsules. 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. 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 a chill affects different men in an indefinite manner, according to their state of body or constitution, causing coughs or colds, rheumatism, or inflammations of various organs.

↑ 2 blocks not present in 1859 1860 1861 1866; present in 1869 1872

With respect to what I have called the indirect action of changed conditions, namely, through the reproductive system being affected, we may infer that variability is thus induced, partly from the fact of this system being extremely sensitive to any change in the conditions, and partly from the similarity, as Kölreuter and others have remarked, between the variability which follows from the crossing of distinct species, and that which may be observed with all plants and animals when reared under new or unnatural conditions. Many facts clearly show how eminently susceptible the reproductive system is to very slight changes in the surrounding conditions.

→ many cases when the 1859 1860 1861 1866

OMIT 1869 1872

→ living long under not very close confinement 1859 1860 1861 1866

kept in an almost free state 1869 1872

→ attributed 1859 1860 1861 1866

but erroneously, attributed 1869 1872

→ discovered that 1860 1861 1866

found out that 1859

discovered that a 1869 1872

→ enter on the copious 1859 1860 1861 1866

give the 1869 1872

→ on 1859 1860 1861 1866

and elsewhere published on 1869 1872

No case is on record of a variable

organism

being

ceasing to

vary

be variable

under cultivation. Our oldest cultivated plants, such as wheat, still

~~often~~

often

yield new varieties: our oldest domesticated animals are still capable of rapid improvement or modification. ↑

It has been disputed at what period of life the causes of variability, whatever they may be, generally act; whether during the early or late period of development of the embryo, or at the instant of conception. ↑ Geoffroy St. Hilaire's experiments show that unnatural treatment of the embryo causes monstrosities; and monstrosities cannot be separated by any clear line of distinction from mere variations. But I am strongly inclined to suspect that the most frequent cause of variability may be attributed to the male and female reproductive elements having been affected prior to the act of conception. Several reasons make me believe in this; but the chief one is the remarkable effect which confinement or cultivation has on the

functions

function

of the reproductive

system;

system:

this system appearing to be far more susceptible than any other part of the organisation, to the action of any change in the conditions of life. Nothing is more easy than to tame an animal, and few things more difficult than to get it to breed freely under confinement, even

when

the →many cases when the male and female unite. How many animals there are which will not breed, though →living long under not very close confinement in their native country! This is

generally,

generally

→attributed to vitiated

instincts.

instincts;

~~but how~~

but how

Many

many

cultivated plants display the utmost vigour, and yet rarely or never seed! In some few

~~such~~

such