- Paperback: 250 pages
- Publisher: Unknown (17 Aug 2009)
- Language English
- ISBN-10: 0217827624
- ISBN-13: 978-0217827621
- Product Dimensions: 1.5 x 2.3 x 0.2 cm
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Product Description
Product Description
This historic book may have numerous typos, missing text, images, or index. Purchasers can download a free scanned copy of the original book (without typos) from the publisher. 1908. Not illustrated. Excerpt: ... CHAPTER IX. OTHER THEORIES OF SPECIES-FORMING AND DESCENT (CONTINUED): AUXILIARY THEORIES (CONTINUED). Isolation Theories.--The varying importance attributed by different biologists to the theories explaining means and results of isolation is notable. While by thoTsda^on" °f some the species-forming influence of isolation faotor imperial- is held to be as effective as selection itself,-- forming. some deem it more effective,--others attach but little importance to it, indeed see no effects of consequence. These latter men are likely to be morphologists, cytologists, and laboratory men generally; the former are systematists, students of distribution, and so-called field naturalists. Thus Delage, who gives much attention in his general discussion of the theories of heredity, variation, and species-forming to many purely speculative theories of the ultimate structure and behaviour of protoplasm, and of the mechanism of heredity, dismisses the whole subject of geographic and topographic isolation with a couple of superficial paragraphs, in which he presents a singularly fallacious statement of what the effects of isolation should be. On the other hand the veteran German world-voyager and exploring naturalist, Moritz Wagner, established long ago, on the basis of his observations and deductions, a "law" of species-forming by migration and consequent isolation, which in his mind makes the natural selection theory superfluous. And Henry Seebohm in a discussion of Romanes's 1 formulation of the principle of physiological selection, says: "So far as is known, no species (of birds) has ever been differentiated without the aid of geographical isolation, though evolution may have gone on to an unknown extent; and, so far as we can judge, geographical isolation ...
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