Helping San Diego, California and beyond since 1997.
Do you need
volunteer, community service, work, military or court hours?
|
|
Helping San Diego, California and beyond since 1997.
|
|
Click here and add this page to your favorites!
|
Encyclopedia Britannica - Main :: LAP-LEO |
|
|
LAW OF THE INDEPENDENT ADAPTIVE EVOLUTION OF PARTS . FIG. II.Diagram demonstrating that there are an indefinite number of combinations of various adaptive types of limbs and feet with various adaptive types of teeth, and that there is no fixed law of correlation between the two series of adaptations.All these principles are consistent with Francis Galton's law of particulate inheritance in heredity, and with the modern doctrine of " unity of characters " held by students of Mendelian phenomena. Sudden versus Gradual Evolution of Parts.There is a broad and most interesting analogy between the evolution of parts of animals and of groups of animals studied as a whole. Thus we observe persistent organs and persistent types of animals, analogous organs and analogous types of animals, and this analogy applico still further to the rival and more or less contradictory hypotheses of the sudden as distinguished from the gradual appearance of new parts or organs of animals, and the sudden appearance of new types of animals. The first exponent of the theory of sudden appearance of new parts and new types, to our knowledge, was Geoffroy St Hilaire, who suggested saltatory evolution through the direct action of the environment on development, as explaining the abrupt transitions in the Mesozoic Crocodilia and tho origin of the birds from the reptiles.Waagen's law of mutation or the appearance of new parts or organs so gradually than they can be perceived only by following them through > lccessive geologic time stages, appears to be directly contradictory to the saltation principle; it is certainly one of the most firmly established principles of palaeontology, and it constitutes the contribution par excellence of this branch of zoology to the law of evolution, since it is obvious that it could not possibly have been deduced from comparison ofliving animals but only through the long perspective gained by comparison of animals succeeding each other in time. The essence of Waagen's law is orthogenesis, or evolution in a definite direction, and, if there does exist an internal hereditary principle controlling such orthogenetic evolution, there does not appear to be any essential contradiction between its gradual operation in the " mutations of Waagen " and its occasional hurried operation in the " mutations of de Vries," which are by their definition discontinuous or saltatory (Osborn, 1907).1. Origin from Primitive or Stem Forms.As already observed, the same principles apply to groups of animals as to organs and groups of organs; an organ originates in a primitive and unspecialized stage, a group of animals originates in a primitive or stem form. It was early perceived by Huxley, Cope and many others that Cuvier's broad belief in a universal progression was erroneous, and there developed the distinction between " persistent primitive types " (Huxley) and " progressive types." The theoretical existence of primitive or stem forms was clearly perceived by Darwin, but the steps by which the stem form might be restored were first clearly enunciated by Huxley in 188o (" On the Application of Evolution to the Arrangement of the Vertebrata and more particularly of the Mammalia ," Scient. Mem. iv. 457) namely, by sharp
original
Wyoming
In certain cases the character stem forms actually survive in unspecialized types. Thus the analysis of George Baur of the ancestral form of the lizards, mosasaurs, dinosaurs, crocodiles and phytosaurs led both to the generalized Palaeohatteria of the Permian and indirectly to the surviving Tuatera lizard of New Zealand. 2. Adaptations to Alternations of Habitat. Law of Irreversibility of Evolution.In the long vicissitudes of time-and procession of continental changes, animals have been subjected to alternations of habitat either through their own migrations or through the " migration of the environment itself," to employ Van den Broeck's epigrammatic description of the profound and sometimes sudden environmental changes which may take place in a single locality. The traces of alternations of adaptations corresponding to these alternations of habitat are recorded both in palaeontology and anatomy, although often after the obscure analogy of the earlier and later writings of a palimpsest. Huxley in 188o briefly suggested the arboreal origin, or primordial tree-habitat of all the marsupials, a suggestion abundantly confirmed by the detailed studies of Dollo and of Bensley, according to which we may imagine the marsupials to have passed through (I) a former terrestrial phase, followed by (2) a primary arboreal phaseillustrated in the tree phalangersfollowed by (3) 5, secondary terrestrial phaseillustrated in the kangaroos and wallabiesfollowed by (4) a secondary arboreal phaseillustrated in the tree kangaroos. Louis Dollo especially has Fish CARNIVOROUS- Flesh Carrion Aquatic Unguligrade ADAPTIVE TYPES OF TEETH OMNIVOROUS HERBIVOROUS -Grass Herb Shrub Fruit Root MYRMECOPHAGOUS Dentition reduced NATATORIAL Amphibious End of Article: LAW OF THE INDEPENDENT ADAPTIVE EVOLUTION OF PARTS If you wish, you can link directly to this article.
<a href="http://jcsm.org/StudyCenter/Encyclopedia/LAP_LEO/LAW_OF_THE_INDEPENDENT_ADAPTIV.html"> LAW OF THE INDEPENDENT ADAPTIVE EVOLUTION OF PARTS </a> |
|
|
(Previous) LAW MERCHANT |
(Next) LAW RELATING TO |
|
Sponsored Advertisements