M Database Inspector (cheetah)
Not logged in. Login


28 rows, page 1 of 7 (4/p)
1 2 3 4 5 6 7

Export to Excel select * from OriginOfSpecies where title like '%summary%' order by subject limit 4 (Page 1: Row)
subject Desending Order (top row is first)
title
ordinal
description
01 - Variations Under Domestication 01-13 - Summary 10 To sum up on the origin of our domestic races of animals and plants.

Changed conditions of life are of the highest importance in causing variability, both by acting directly on the organisation, and indirectly by affecting the reproductive system.

It is not probable that variability is an inherent and necessary contingent, under all circumstances.

The greater or less force of inheritance and reversion, determine whether variations shall endure.

Variability is governed by many unknown laws, of which correlated growth is probably the most important.

Something, but how much we do not know, may be attributed to the definite action of the conditions of life. Some, perhaps a great, effect may be attributed to the increased use or disuse of parts.

The final result is thus rendered infinitely complex.

In some cases the intercrossing of aboriginally distinct species appears to have played an important part in the origin of our breeds.

When several breeds have once been formed in any country, their occasional intercrossing, with the aid of selection, has, no doubt, largely aided in the formation of new sub-breeds; but the importance of crossing has been much exaggerated, both in regard to animals and to those plants which are propagated by seed.
01 - Variations Under Domestication 01-13 - Summary 20 With plants which are temporarily propagated by cuttings, buds, &c., the importance of crossing is immense; for the cultivator may here disregard the extreme variability both of hybrids and of mongrels, and the sterility of hybrids; but plants not propagated by seed are of little importance to us, for their endurance is only temporary.

Over all these causes of Change, the accumulative action of Selection, whether applied methodically and quickly, or unconsciously and slowly but more efficiently, seems to have been the predominant Power.

Charles Darwin
Charles Darwin
02 - Variations Under Nature 02-07 - Summary 20 In all these respects the species of large genera present a strong analogy with varieties. And we can clearly understand these analogies, if species once existed as varieties, and thus originated; whereas, these analogies are utterly inexplicable if species are independent creations.

We have, also, seen that it is the most flourishing or dominant species of the larger genera within each class which on an average yield the greatest number of varieties; and varieties, as we shall hereafter see, tend to become converted into new and distinct species.

Thus the larger genera tend to become larger; and throughout nature the forms of life which are now dominant tend to become still more dominant by leaving many modified and dominant descendants.

But by steps hereafter to be explained, the larger genera also tend to break u into smaller genera. And thus, the forms of life throughout the universe become divided into groups subordinate to groups.
02 - Variations Under Nature 02-07 - Summary 10 Finally, varieties cannot be distinguished from species,- except, first, by the discovery of intermediate linking forms; and, secondly, by a certain indefinite amount of difference between them; for two forms, if differing very little, are generally ranked as varieties, notwithstanding that they cannot be closely connected; but the amount of difference considered necessary to give to any two forms the rank of species cannot be defined.

In genera having more than the average number of species in any country, the species of these genera have more than the average number of varieties.

In large genera the species are apt to be closely, but unequally, allied together, forming little clusters round other species. Species very closely allied to other species apparently have restricted ranges.