Biology Reference
In-Depth Information
governed by a selective mechanism, but this selection is purely inter-
nal to the organism. It does not reflect the external selective constraint
which is exerted on the embryo, as is the case in ontophylogenesis
(see Figs. 16 and 17).
We believe that the metaphor of the ecosystem can be used to
describe the relationships concerning metabolic exchange between
the cells
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but, like any metaphor, it should be used sparingly
because it may be dangerous. On the one hand it helps in under-
standing an aspect of the phenomenon, but on the other it induces
misinterpretations. Embryogenesis cannot be reduced to this.
Ontophylogenesis is a process not of self-organisation but of hetero-
organisation, in which environmental constraints are essential. In
addition, in this process DNA also retains a primordial role for
which there is no equivalent in an ecosystem. It does not just pas-
sively provide the proteins which the cell needs. The way it func-
tions, although probabilistic, involves rules allowing it to have an
influence on the organism (see the following sections of this chap-
ter). This point of view is moreover supported by the result of the
simulations. When autostabilisation is eliminated and cells are
reduced to their metabolic exchange relationships, as occurs in an
ecosystem, they lose their properties for organisation (Fig. 27C).
That does indeed suggest that biological organisation depends on
equilibrium, but it is not a prey/predator (ecological) type of equi-
librium between the parts of the organism. It is equilibrium
between the equivalent of two forces: the pressure of selection that
is exerted on biological structures, and the random non-specificity
of molecular interactions which makes them variable.
6.5
Models of gene expression
If, as we believe, DNA plays an important role without it being that
of a genetic programme, we must define it more exactly, which we
shall now do.
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This metaphor is in fact similar to that of the organism considered as an eco-
nomic system, used by Bernard right from the 19th century (see this chapter, ยง6.1.3),
of which there are very many variants.
