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absence adaptation American animals appear base become bees body breeding called cells changes characters color conclusion corn course crossed Darwin described determined difficult discussion dk.br effect eggs environment evidence evolution exist experiments fact factor female fertilization flowers forms further gametophytes give given green growing growth hair important increase indicate individuals inheritance insects interesting kind known leaves less light male matter means measurements Mendelian methods mutation natural normal Notes observed occur organs origin pairs parent plants Pleistocene possible present probably problem produced Professor pure question race reason recent reference regard region relation represented Science seems selection side single soil species stages structure theory tion true unit variability variations varieties various vegetation visits whole yellow
Página 78 - But as my conclusions have lately been much misrepresented, and it has been stated that I attribute the modification of species exclusively to natural selection, I may be permitted to remark that in the first edition of this work, and subsequently, I placed in a most conspicuous position — namely, at the close of the Introduction — the following words : " I am convinced that natural selection has been the main but not the exclusive means of modification.
Página 69 - No man would ever try to make a fantail till he saw a pigeon with a tail developed in some slight degree in an unusual manner, or a pouter...
Página 135 - We are thus brought to the question which has been largely discussed by naturalists, namely, whether species have been created at one or more points of the earth's surface. Undoubtedly there are very many cases of extreme difficulty, in understanding how the same species could possibly have migrated from some one point to the several distant and isolated points, where now found. Nevertheless the simplicity of the view that each species was first produced within a single region captivates the...
Página 81 - Our ignorance of the laws of variation is profound. Not in one case out of a hundred can we pretend to assign any reason why this or that part differs, more or less, from the same part in the parents.
Página 79 - One of the most remarkable features in our domesticated races is that we see in them adaptation, not indeed to the animal's or plant's own good, but to man's use or fancy.
Página 377 - ... 1 Papers from the Biological Laboratory of the Maine Agricultural Experiment Station. No.
Página 141 - The direct action of changed conditions leads to definite or indefinite results. In the latter case the organisation seems to become plastic, and we have much fluctuating variability. In the former case the nature of the organism is such that it yields readily, when subjected to certain conditions, and all, or nearly all the individuals become modified in the same way.
Página 138 - ... to natural selection, by affording a better chance of the occurrence of profitable variations. Unless such occur, natural selection can do nothing. Under the term of " variations," it must never be forgotten that mere individual differences are included.
Página 77 - There are, however, some who still think that species have suddenly given birth, through quite unexplained means, to new and totally different forms: but, as I have attempted to show, weighty evidence can be opposed to the admission of great and abrupt modifications. Under a scientific point of view, and as leading to further investigation, but little advantage is gained by believing that new forms are suddenly developed in an inexplicable manner from old and widely different forms, over the old...