Evolution and AdaptationMacmillan, 1903 - 470 pages |
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Common terms and phrases
acquired characters adaptation adult advantage amongst animals and plants aphids appear arisen artificial selection assume become believe birds breed butterflies caterpillars causes cells chromosomes color connection crawl crustaceans Darwin Darwinian degeneration degrees descendants determined direction elementary species embryo environment evidence evolution examine exist experiments explain fact fertilized eggs flowers fluctuating variations gemmules geotropic germ-cells give heliotropic hybrid hypothesis important individuals inheritance of acquired insects instance instinct kinds Lamarck Lamarckian large number larvæ later leaves less light living long-styled male and female mammals ment moths mutation theory Nägeli natural selection nest offspring organs origin outcome pangenesis parent form parthenogenetic polar body pollen probable produced question race reproduction resemblance response result rotifers seeds sexual reproduction sexual selection shown side sort spermatozoon stages stamens structure supposed surface takes place tion tropisms tube variability varieties Vries Weismann wings young
Popular passages
Page 117 - If such do occur, can we doubt (remembering that many more individuals are born than can possibly survive) that individuals having any advantage, however slight, over others, would have the best chance of surviving and of procreating their kind ? On the other hand, we may feel sure that any variation in the least degree injurious would be rigidly destroyed. This preservation of favourable individual differences and variations, and the destruction of those which are injurious, I have called Natural...
Page 131 - To suppose that the eye, with all its inimitable contrivances for adjusting the focus to different distances, for admitting different amounts of light, and for the correction of spherical and chromatic aberration, could have been formed by natural selection, seems, I freely confess, absurd in the highest possible degree.
Page 116 - When we reflect on this struggle, we may console ourselves with the full belief, that the war of nature is not incessant, that no fear is felt, that death is generally prompt, and that the vigorous, the healthy, and the happy survive and multiply.
Page 116 - Can the principle of selection, which we have seen is so potent in the hands of man, apply under nature? I think we shall see that it can act most efficiently. Let the endless number of slight variations and individual differences occurring in our domestic productions, and, in a lesser degree, in those under nature, be borne in mind ; as well as the strength of the hereditary tendency.
Page 113 - 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.
Page 119 - ... be, compared with those accumulated by nature during whole geological periods. Can we wonder, then, that nature's productions should be far "truer" in character than man's productions; that they should be infinitely better adapted to the most complex conditions of life, and should plainly...
Page 129 - LONG before the reader has arrived at this part of my work, a crowd of difficulties will have occurred to him. Some of them are so serious that to this day I can hardly reflect on them without being in some degree staggered...
Page 117 - Variations neither useful nor injurious would not be affected by natural selection, and would be left either a fluctuating element, as perhaps we see in certain polymorphic species, or would ultimately become fixed, owing to the nature of the organism and the nature of the conditions.
Page 116 - Can it, then, be thought improbable, seeing that variations useful to man have undoubtedly occurred, that other variations, useful in some way to each being in the great and complex battle of life, should occur in the course of many successive generations ? If such do occur, can we doubt (remembering that many more...
Page 108 - Again, it may be asked, how is it that varieties, which I have called incipient species, become ultimately converted into good and distinct species, which in most cases obviously differ from each other far more than do the varieties of the same species...