Origin of Species Variorum

Comparison with 1866

do believe that natural selection always acts very slowly, generally at only long intervals of time, and generally on only a very few of the inhabitants of the same region at the same time. I further believe, that this slow, intermit- tent action of natural selection accords perfectly .. with what geology tells us of the rate and manner at which the inhabitants of this world have changed.

Slow though the process of selection may be, if feeble man can do much by his powers of artificial selection, I can see no limit to the amount of change, to the beauty and infinite complexity of the coadaptations between all organic beings, one with another and with their physical conditions of life, which may be effected in the long course of time by nature's power of selection.

Extinction .—

This subject will be more fully discussed in our chapter on Geology; but it must be here alluded to from being intimately connected with natural selection. Natural selection acts solely through the preservation of variations in some way advantageous, which consequently endure. From the high geometrical ratio of increase of all organic beings, each area is already .. stocked with the full number of its existing inhabitants, and as most areas are already stocked with a great diversity of forms, it follows that, as each selected and favoured form increases in number, so generally will the less favoured forms decrease and become rare. Rarity, as geology tells us, is the precursor to extinction. We can, also, see that any form represented by few individuals will, during fluctuations in the seasons or in the number of its enemies, run a good chance of utter extinction. But we may go further than this; for as new forms are continually and slowly being produced, unless we believe that the number of specific forms goes on perpetually and almost indefinitely increasing, many inevitably must become extinct. That the number of specific forms has not indefinitely increased, geology tells us plainly; and we shall presently attempt to show why it is that the number of places in the polity of nature is not indefinitely great,— not that we have any means of knowing that any one region has as yet got its maximum of species. ↑

Furthermore, the species which are most numerous in individuals will have the best chance of producing within any given period favourable variations. We have evidence of this, in the facts given in the second chapter, showing that it is the common species which offer the greatest number of recorded varieties, or incipient species. Hence, rare species will be less quickly modified or improved within any given period, and they will consequently be beaten in the race for life by the modified descendants of the commoner species.

From these several considerations I think it inevitably follows,

do believe that natural selection will generally act very slowly, only at long intervals of time, and only on .. a .. few of the inhabitants of the same region. .. .. .. .. I further believe that these slow, intermittent results accord well with what geology tells us of the rate and manner at which the inhabitants of the world have changed.

Slow though the process of selection may be, if feeble man can do much by ... artificial selection, I can see no limit to the amount of change, to the beauty and .. complexity of the coadaptations between all organic beings, one with another and with their physical conditions of life, which may have been affected in the long course of time through nature's power of selection, that is by the survival of the fittest.

Extinction caused by Natural Selection.

This subject will be more fully discussed in our chapter on Geology; but it must here be alluded to from being intimately connected with natural selection. Natural selection acts solely through the preservation of variations in some way advantageous, which consequently endure. Owing to the high geometrical rate of increase of all organic beings, each area is already fully stocked with inhabitants; and it follows from this, that as the favoured forms increase in number, so, generally, will the less favoured .. decrease and become rare. Rarity, as geology tells us, is the precursor to extinction. We can .. see that any form which is represented by few individuals will run a good chance of utter extinction, during great fluctuations in the nature of the seasons, or from a temporary increase in the number of its enemies. .. .. .. .. .. .. .. But we may go further than this; for, as new forms are ... produced, unless we admit that ... specific forms can go on indefinitely increasing in number, many old forms must become extinct. That the number of specific forms has not indefinitely increased, geology plainly tells us; and we shall presently attempt to show why it is that the number of species throughout the world has not become immeasurably great. ↑

We have seen that the species which are most numerous in individuals have the best chance of producing favourable variations within any given period. We have evidence of this, in the facts stated in the second chapter, showing that it is the common and diffused or dominant species which offer the greatest number of recorded varieties. .. .. .. Hence, rare species will be less quickly modified or improved within any given period; .. they will consequently be beaten in the race for life by the modified and improved descendants of the commoner species.

From these several considerations I think it inevitably follows,