The American Naturalist, Volumen43Essex Institute, 1909 |
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Página 48
... race . The mammoth fed on tree trunks which he ground with his teeth , and in a short time the whole North of Siberia was deprived of trees . Hence is the origin of the northern tundra . In the be- ginning the earth had the form of an ...
... race . The mammoth fed on tree trunks which he ground with his teeth , and in a short time the whole North of Siberia was deprived of trees . Hence is the origin of the northern tundra . In the be- ginning the earth had the form of an ...
Página 50
... racing . Other things being equal , an old stallions ' colts would inherit greater dynamic development and be faster than other colts sired by the same horse while younger . He found that the average trotting - bred horses , represented ...
... racing . Other things being equal , an old stallions ' colts would inherit greater dynamic development and be faster than other colts sired by the same horse while younger . He found that the average trotting - bred horses , represented ...
Página 68
... races by this method of saltation , there can be no doubt that he entertained a strong bias in favor of the evolution of species generally by slow and minute steps . As far as cultivated plants and domesticated animals were concerned ...
... races by this method of saltation , there can be no doubt that he entertained a strong bias in favor of the evolution of species generally by slow and minute steps . As far as cultivated plants and domesticated animals were concerned ...
Página 70
... race of tumbler pigeons actually tumbled - that is to say , they were mutants . As to the origin of domestic races through modifications so abrupt as to have been thought by Darwin entirely independent of selection , he gave it as his ...
... race of tumbler pigeons actually tumbled - that is to say , they were mutants . As to the origin of domestic races through modifications so abrupt as to have been thought by Darwin entirely independent of selection , he gave it as his ...
Página 73
... race conforming to his own test of a species , namely its possession of " the power of remaining for a good long period constant . . . combined with an appreciable amount of difference ' '13 One of the most striking of these cases is ...
... race conforming to his own test of a species , namely its possession of " the power of remaining for a good long period constant . . . combined with an appreciable amount of difference ' '13 One of the most striking of these cases is ...
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absence adaptation American animals appear bees breeding brown cells cent chromosomes corn plant correlation crinoids crossed curve Darwin dk.br dominant ecology eggs elementary species environment evidence evolution experimental experiments fact factors fertilization flowers fluctuating forms gametes genus green growth gynandromorphs hair color heredity heterozygote hybrids important index number individuals inheritance insects kelps L. H. BAILEY lamina large number larva larvæ Lessoniopsis lt.br male Mendelian Mendelian inheritance methods morphology muscular articulations mutation natural selection Notes and Literature observed offspring organs origin Origin of Species oyster pairs pangen paper Paramecium parent physiological pigment pinnule present problem produced Professor pure race RAYMOND PEARL rays Recapitulation Theory recent region relation Science seems selection index single sired specimens sporophytic stipe structure T. H. MORGAN theory tion unit characters variability variations varieties vegetation Vries yellow
Pasajes populares
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 156 - If numerous species, belonging to the same genera or families, have really started into life at once, the fact would be fatal to the theory of evolution through natural selection.
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...