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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 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 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 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.
Page 106 - ... manner as here put. I always thought individual differences more important ; but I was blind and thought that single variations might be preserved much oftener than I now see is possible or probable. I mentioned this in my former note merely because I believed that you had come to a similar conclusion, and I like much to be in accord with you. I believe I was mainly deceived by single variations offering such simple illustrations, as when man selects.
Page 101 - ... 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 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 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).
Page 145 - Without Isolation, or the prevention of free intercrossing, organic evolution is in no case possible. Therefore it is Isolation that has been ' the exclusive means of modification,' or more correctly, the universal condition to it. Therefore, also, heredity and variability being given, the whole theory of organic evolution becomes a theory of the causes and conditions which lead to isolation.