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.
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).