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Amixia animals apogamy arise artificial selection associated average breeding cause cents closely allied species common areas condition crossing Darwin Darwinian discriminate distinction divergence of character divergence of type divergent evolution effects of intercrossing evidence fact factor flowers form of homogamy form of isolation free intercrossing genera geographical isolation groups Gulick heredity hybrids importance indiscriminate isolation infertility insect visits inter large number Lloyd Morgan logical modification molluscs monotypic and polytypic monotypic evolution Moritz Wagner mutual sterility natural selection number of individuals occur organic evolution origin of species paper parent form Paul Carus peculiarity physio physiological change physiological isolation physiological selection pollen polytypic evolution prepotency present prevention of intercrossing principle Prof progeny question regard reproductive system result segregation selective fertility separated sexual specific characters specific differentiation specific divergence specific type supposed swamping effects synoical theory of natural theory of physiological tion variability variations varieties Wagner Wallace Wallace's Weismann
Page 87 - Composita? exist, and there can be no doubt that if the pollen of all these species could be simultaneously or successively placed on the stigma of any one species, this one would elect with unerring certainty its own pollen.
Page 181 - An Illustrated Monthly Magazine Devoted to the Science of Religion, The Religion of Science and the Extension of The Religious Parliament Idea THE OPEN COURT is a popular magazine discussing the deepest questions of life. It offers the maturest thought in the domains of Religion, Philosophy, Psychology, Evolution and kindred subjects. THE OPEN COURT contains articles on the recent discoveries of Babylonian and Egyptian excavations, on Old Testament Research...
Page 51 - ONE of the greatest, or perhaps we may say the greatest, of all the difficulties in the way of accepting the theory of natural selection as a complete explanation of the origin of species, has been the remarkable difference between varieties and species in respect of fertility when crossed.
Page 15 - ... the initial differences are for ever reacting on the environment and on each other in such a way as to...
Page 134 - ... alone in an otherwise undifferentiated species ' " ; therefore, " even if I am wrong in supposing that physiological selection can ever act alone, the principle of physiological selection, as I have stated it, is not thereby affected. And this principle is, as Mr. Wallace has re-stated it, 'that some amount of infertility characterizes the distinct varieties which are in process of differentiation into species...
Page 99 - ... some changes in the external conditions. This will justly sound very hypothetical. I cannot give my reasons in detail ; but the most general conclusion, which the geographical distribution of all organic beings, appears to me to indicate, is that isolation is the chief concomitant or cause of the appearance of new forms (I well know there are some staring exceptions).
Page 27 - The proof of the 2nd is found wherever a set of closely allied organisms is so distributed over a territory that each species and variety occupies its own narrow district, within which it is shut by barriers that restrain its distribution, while each species of the environing types is distributed over the whole territory. The distribution of terrestrial molluscs on the Sandwich Islands presents a great body of facts of this kind.
Page 172 - the consequences of fertilization reach their optimum when a certain mean difference in the origin of the sexual cells is attained," and by Fritz Miiller that " every plant requires, for the production of the strongest possible and most prolific progeny, a certain amount of difference between male and female elements which unite. Fertility is diminished as well when this degree is too low (in relatives too closely related) as when it is too high (in those too little related).