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Theory of evolution

 

Aristotle thought that the alive beings had been created separately and who later they were changing due to a improver principle. The fossil encounter proposed the catastrophic theory that says "the life has been created often by different factors". The forms that had died were replaced by other new something different. Buffon in century XVIII indicated that the ideas of Aristotle were not certain, Darwin add that the answers given to the external stimuli were inherited, Lamarck was first in publishing the general theories of the evolution indicating that the animals divided themselves in: vertebrates and invertebrates.

The theory of the inheritance of caractéres seted out acquired: the present organisms and the parts that compose it tend to increase of size; if an organ is used constantly it tends to increase of size and the lack of use gives rise to the degeneration; the appearance of a new organ is always from a necessity; these modifications will be inherited being that the changes are cumulative. The theory of Lamarck was rejected because it was not managed to verify his ideas.

Heckel in 1821 said that the superior animal embryos happened through stages that were resembled those of the inferior ones. Van Baer (1829), indicated that the inferior and superior animal embryos are very similar to the corresponding ones in their adult stages, being based on which: the general characters of all alive being appear before the special characters, the characters of an alive being appear in order: greatest, less general, the special ones; an animal during its development leaves the form of other animals progressively; the young stages of a superior animal are like the embryos of the inferior ones.

NATURAL SELECTION

In 1858 works were published in which it appeared a new concept of evolution, the theory of the natural selection, cradle in the principles of the evolution. Wallace, realized equipped survival of the best one, publicón a work "about the tendency of the varieties to separate indefinitely from the original type", next to Darwin tried to obtain the greater number of tests on the matter. In the 1859 Darwins the origin of the species by means of the natural selection or the preservation of races privileged in the fight by the life published all its discoveries in the book "". The theory of Darwin is transformed: more plants take place and animals of which really they survive, exist variations of all type in the alive beings, is a fight by the existence and since result is always a conservation of the privileged races.

After appearing these ideas there were biologists that criticized them because they were not explained as they passed the variations to the descendants. In the 1868 Darwins it explained this by means of the theory of the Pangenes, in which it supposed that all the organs and perhaps all the cells produced miniatures of they themselves in the body of the animal, to these miniatures called Pangenes or gémulas to him, these they were spilled to the blood that took them glands to the sexual and there were associated to form the sexual cells. Of this form the environmental changes produced modified modified organs and these pangenes were transmitted to the following generation. Galton in 1857 demonstrated that this was not certain. Then there were scientists who accepted the ideas of Darwin, to this time denominated romantic period to him (Darwinist), examples were: Huxley, Spencer... Later arose another time at which it was criticized and agnostic period was denominated (time in which they appeared the laws of Mendel).

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