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. (查看原文)
I may add, that when under nature the conditions oflife do change, variations and reversions of character prob-ably do occur, but natural selection, as will hereafter be explained, will determine how far the new characters thus arising shall be preserved. (查看原文)
Over all these causes of Change I am con-vinced that the accumulative action of Selection, whetherapplied methodically and more quickly, or unconsciouslyand more slowly, but more efficiently, is by far the predoinant Power. (查看原文)
No one supposes thatall the individuals of the same species are cast in the verysame mould. These individual differences are highly important for us, as they afford materials for natural selectionto accumulate, in the same manner as man can accumulateIn any given direction individual differences in his domesticated productions. (查看原文)
Where many large trees grow, we expect to find saplings. Where many species of a genus have been formed through variation, circumstances have been favourable for variation; and hence we might expect that the circumstances would generally be still favourable to variation. On the other hand, if we look at each species as a special act of creation, there is no apparent reason why more varieties should occur in ao group having many species, than in one having few. (查看原文)
And we can clearly understand these analogies, if species have once existed as varieties, and have thus originated: whereas, these analogies are utterly inexplicable if each species has been independently created. (查看原文)
Owing to this struggle for life, any variation, however slight and from whatever cause proceeding, if it be in an degree profitable to an individual of any species, in its infinnitely complex relations to other organic beings and tod external nature, will tend to the preservation of that individual, and will generally be inherited by its offspring. (查看原文)
Battle within battle must ever berecumng with varying success; and yet in the long-run theforces are so nicely balanced, that the face of nature remains uniform for long periods of time, though assuredlythe merest trifle would often give the victory to one organicheing over another. Nevertheless so profound is our igno-rance, and so high our presumption, that we marvel whenwe hear of the extinction of an organic being: and as we donot see the cause, we involve cataclysms to desolate theworld or invest laws on the duration of the forms of life! (查看原文)
This preservation of favourable Hlae asivariations and the rejection of injurious variations, I call utangNatural Selection. Variations neither useful nor injurious would not be affected by natural selection, and would be
left a fluctuating element, as perhaps we see in the sproles agttcalled polymorphic. (查看原文)
Hence I am inclined to look at adaptation to any special climate as a quality readily grafted on an innate wide flexibility of constitution, which is common to most animals. (查看原文)
After the foregoing discussion, which ought to have been much amplified, we may, I think, assume that the modified descendants of any one species will succeed by so much the better as they become more diversified in structure, and are thus enabled to encroach on places occupied by other beings. (查看原文)
I am strongly inclined to suspect that, both in the vegetable and animal kingdoms, an occasional intercross with a distinct individual is a law of nature...
Finally then, we may conclude that in many organic beings, a cross between two individuals is an obvious necessity for each birth: in many others it occurs perhaps only at long intervals, but in none, as I suspect, can self-fertilisation go on for perpetuity. (查看原文)
On the whole, I think we may conclude that habit, use,and disuse, have, in some cases, played a considerable partin the modification of the constitution. and of the structureof various organs; but that the effects of use and disuse haveoften been largely combined with, and sometimes overmastered by, the natural selection of innate differences. (查看原文)
