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20.05.2021 | History

1 edition of Three papers on the tendency of species to form varieties found in the catalog.

Three papers on the tendency of species to form varieties

and on the perpetuation of varieties and species by natural means of selection.

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      • Caption title.Running title: Tendency of species to form varieties.Photocopy from: Zoologist.London, 1858, v. 16.Cf. Freeman 349 and 1700.

        LC Classifications1950
        The Physical Object
        Paginationxvi, 53 p. :
        Number of Pages44
        ID Numbers
        ISBN 10nodata

        nodata File Size: 8MB.

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Three papers on the tendency of species to form varieties by s.n. Download PDF EPUB FB2

Now I think it cannot be doubted that during the breeding-season all the mice with the exception of a few males or females in excess ordinarily pair, and therefore that this astounding increase during three years must be attributed to a greater number than usual surviving the first year, and then breeding, and so on till the third year, when their numbers were brought down to their usual limits on the return of wet weather.

But how important an element enclosure is, I plainly saw near Farnham, in Surrey. The amount of food for each species of course gives the extreme limit to which each can increase; but very frequently it is not the obtaining food, but the serving as prey to other animals, which determines the average numbers of a species. Natura non facit saltum answers some of the most obvious. In the majority of cases it is most difficult to imagine where the checks fall—though generally, no doubt, on the seeds, eggs, and young; but when we remember how impossible, even in mankind so much better known than any other animalit is to infer from repeated casual observations what the average duration of life is, or to discover the different percentage of deaths to births in different countries, we ought to feel no surprise at our being unable to discover where the check falls in any animal or plant.

The Darwin-Wallace paper occurs in the complete part in blue wrappers, or in the Zoology part in pink wrappers; the Botany parts were in green. The action of this principle is exactly like that of the centrifugal governor of the steam engine, which checks and corrects any irregularities almost before they become evident; and in like manner no unbalanced deficiency in the animal kingdom can ever reach any conspicuous magnitude, Three papers on the tendency of species to form varieties it would make itself felt at the very first step, by rendering existence difficult and extinction almost sure soon to follow.

The 1858 Darwin

There is no muscle of its body that is not called into daily and hourly activity; there is no sense or faculty that is not strengthened by continual exercise. An abstract of a private letter addressed to Professor Asa Gray, of Boston, U. Our familiarity with the larger domestic animals tends, I think, to mislead us: we see no great destruction falling on them, and we forget that thousands are annually slaughtered for food, and that in a state of nature an equal number would have somehow to be disposed of.

On the Tendency of Species to form Varieties An introduction by R. Many can, I think, be satisfactorily answered. Now, let some alteration of physical conditions occur in the district—a long period of drought, a destruction of vegetation by locusts, the irruption of some new carnivorous animal seeking "pastures new"—any change in fact tending to render existence more difficult to the species in question, and tasking its utmost powers to avoid complete extermination; it is evident that, of all the individuals composing the species, those forming the least numerous and most feebly organized variety would suffer first, and, were the pressure severe, must soon become extinct.

There must have been also a kind of unconscious selection from a remote period, namely in the preservation of the individual animals without any thought of their offspring most useful to each race of man in his particular circumstances. Lighten any check, mitigate the destruction ever so little, and the number of the species will almost instantaneously increase to any amount.

[Read 1 July] Journal of the Proceedings of the Linnean Society of London. But how false a view is this! What a struggle between the several kinds of trees must here have gone on during long centuries, each annually scattering its seeds by the thousand; what war between insect and insect between insects, snails, and other animals with birds and beasts of prey all striving to increase, and all feeding on each other or on the trees or their seeds and seedlings, or on the other plants which first clothed the ground and thus checked the growth of the trees!