Biology Reference
In-Depth Information
variations in the way it does this. Cell and functional structures act
in the same way in an organism to reduce the macroscopic effect of
the random behaviour of the molecules, without nevertheless elim-
inating it. Proteins are always subjected to thermal agitation, which
permits stochastic variations creating tiny differences between cells
that are the origin of their differentiation.
In the course of evolution, under the pressure of natural selec-
tion in which environmental constraints with an effect on organisms
accumulate, cell structuring has greatly increased. A eukaryotic cell
of a multicellular organism has many more organelles and mem-
branes than a unicellular prokaryotic cell, and this structuring has
reduced molecular randomness. Multicellular organisms have also
become more complex through the creation of structures and func-
tions. Functional structures ensuring the constancy of the internal
environment have been selected because they increase the viability
of the organisms. At the same time, the roles of the DNA and the
structure have come to predominate and the organism has thus
escaped from variability of the environment.
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There are, of course, notable divergences between ontophyloge-
nesis and Bernard's theory. He did not apply his theory to the prob-
lem of ontogenesis which he considered to be too complicated, and
he was a staunch adherent to determinism (Gayon, in press). At the
same period variability was already present, on the other hand, in
Darwin's theory. Darwin thought that it was the variations in
organisms that made it possible for them to adapt to their envi-
ronment. Ontophylogenesis therefore combines aspects of Darwin's
natural selection with Bernard's internal environment.
6.1.3
The organism functions for the cells,
not the reverse
The relationship between the organism and its parts is another
basic question which often leads to confusion. In ontophylogenesis,
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Although its influence remains of considerable importance for many species,
particularly plants.
