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acquired characters adaptive characters adduced animals appears argument argument from ignorance artificial selection become cause cessation of selection chapter climatic co-adaptation colour concerned congenital connexion continuity correlation Darwin Darwinian deduction definition degeneration degree distinction disuse doctrine due to natural epilepsy evidence experiments explain fact favour force of heredity Galton genera germ-plasm hereditary importance individuals inherited effects instincts kind Lamarck Lamarckian factors Lamarckian principles large proportional number less Lloyd Morgan matter merely modifications natural selection naturalists necessarily niata observed occur opinion organic evolution Origin of Species pangenesis panmixia parents particular peculiar plants possible present produced Professor Weismann's progeny prove question reason reflex action reflex mechanism regard remark restiform body reversal of selection sciatic nerve sexual selection somatogenetic specific characters statement structure sufficient suppose theory of heredity theory of natural tion transmission of acquired transmitted use-inheritance utility variations varieties Wallace Wallace's Weismann Weismann's theory
Page 321 - be indispensable for this act ; but as sutures occur in the skulls of young birds and reptiles, which have only to escape from a broken egg, we may infer that this structure has arisen from the laws of growth, and has been taken advantage of in the parturition of the higher animals
Page 320 - In my opinion the greatest error -which I have committed, has been not allowing sufficient weight to the direct action of the environment, ie food, climate, &c., independently of natural selection. Modifications thus caused, which are neither of advantage nor disadvantage to the modified
Page 328 - Or only a third, fifth, or tenth part of the individuals may have been thus affected, of which fact several instances could be given. Thus Graba estimates that about one-fifth of the guillemots in the Faroe Islands consist of a variety so well marked, that it was formerly ranked as a distinct species under the name of Uria
Page 328 - There can be little doubt that the tendency to vary in the same manner has often been so strong, that all individuals of the same species have been similarly modified without the aid of any form of selection
Page 187 - their true plumage after a few generations. An excellent observer (Mr. Hewitt) . . . found that he could not breed wild ducks true for more than five or six generations, as they proved so much less beautiful. The white collar round the neck of the mallard became broader and more irregular, and white feathers appeared in the duckling's wings
Page 323 - I fully admit that many structures are now of no use to their possessors, and may never have been of any use to their progenitors; but this does not prove that they were formed solely for beauty or variety. No doubt the definite action of changed conditions, and the various causes of
Page 182 - there can be little doubt that the tendency to vary in the same manner has often been so strong, that all individuals of the same species have been similarly modified without the aid of any form of selection 1
Page 330 - Each of the endless variations which we see in the plumage of our fowls must have had some efficient cause; and if the same cause were to act uniformly during a long series of generations on many individuals, all probably would be modified in the same manner.
Page 329 - ignorant of the exciting cause of the above specified modifications; but if the unknown cause were to act almost uniformly for a length of time, we may infer that the result would be almost uniform; and in this case all the individuals of the species would be modified in the same manner'.