Biology Reference
In-Depth Information
the system. Millions of molecules move coherently, forming hexag-
onal convection cells of a characteristic size”
(OOC p. 142).
Another example of a dissipative mechanism given by Prigogine
concerns the creation of concentration gradients of morphogen mol-
ecules during embryogenesis. This is a system of coupling between
several chains of chemical reactions in which the various products
of the reactions diffuse with different speeds (OOC pp. 146-153).
In this system the reactions are specific and the concentrations of
the reactants are fixed by interaction with the medium. For certain
values of these concentrations, instead of achieving a classic state
of chemical equilibrium characterised by constant concentrations
of the reaction products the system oscillates in cycles, with the
concentrations varying reproducibly over time and space.
Prigogine's model is in fact similar to Alan Turing's reaction-diffusion
mechanism.
In Prigogine's view, these phenomena provide support for a
holistic philosophy, and in his view, “
This leads to a new view of
matter in which matter is no longer the passive substance described
in the mechanistic world view but is associated with spontaneous
activity
” (OOC pp. 9). The spontaneous emergence of order in dis-
sipative structures bears witness to the creative trend that animates
nature. This is the ordinary holistic principle which is a central
theme of his theory.
Dissipative structures are therefore supposed to explain the cre-
ation of order in living organisms. Can they however explain how
non-specific biological molecules are organised during ontogenesis?
To answer this question several points must be borne in mind.
First of all, the coupled chemical reaction model cannot by def-
inition be relevant, because the chemical reactions brought into
play are specific. What we need is a model which explains the
appearance of order from numerous molecules involved in a great
many non-specific interactions (and reactions), comparable with
biological systems (see chapter 4). How does Bénard's instability
come into this? It is always given as the very prototype of self-
organisation demonstrating that life is thermodynamically possible.
