Biology Reference
In-Depth Information
Of course physics too has undergone a tremendous evolution since the days
of Schrödinger and Carnap (Schrödinger, 1944; Carnap, 1966). It has been rec-
ognized that far away from equilibrium, physical-chemical systems may relax
towards metastable states rather than to equilibrium, and anyway such states are
typically well isolated from each other in the form of local minima as in any
other search landscape (Bäck et al., 1997; Frauenfelder & McMahon, 2001).
The states can be more complex than the equilibrium state, i.e. appear to be
more organized than the latter. Such physical self-organizing systems have been
proposed to be at the basis of the tremendous organization that is observed in
biology. Accordingly, parts of modern physics address the generation and main-
tenance of complex dynamic structures, and how new properties may emerge
from nonlinear dynamic interactions. However the mechanisms that have been
proposed such as the Brussellator (Nicolis & Prigogine, 1977) are themselves
nonverifiable/nonfalsifiable. This is because they were formulated in much too
general terms, causing loss of the specificity of the biological system at hand.
Testing of nonlinear phenomena requires precision, hence a precise matching
of mathematical model and experimental system. Wolf et al. (Wolf et al., 2000)
have recently worked towards such a testing of a proposed self-organization
mechanism for synchronization of the glycolytic oscillations in a population of
yeast cells, but this may only serve as an incomplete example. This brings us
to the second type of understanding, i.e. on the basis not of the principles of
underlying sciences but of principles that are discovered in the science at hand,
i.e. on the basis of newly discovered principles of biological systems. Here there
is the issue whether anything is to be expected from the search for such theories.
Metabolic and hierarchical control analysis are theories that may serve as
examples of theories that are custom-made for biological systems (Westerhoff &
Hofmeyr, 2005). By making an idealized description of intracellular networks,
i.e. metabolic networks for the former theory and gene-expression or signal
transduction networks for the latter, a mathematical set of definitions can be
made and laws can be deduced from the time-transformation invariance and
from stability against fluctuations (cf. Hornberg et al., 2005; Peletier et al., 2003;
Westerhoff & van Dam, 1987). These theories are in a sense comparable to
theories in physics in that they derive from observations that falsified alternative
hypotheses, and led to conjectured new laws, which could then be deduced
from postulated fundamental properties (axioms) of the system. Other 'laws'
that derive more as a result of induction from experimental observations may
also be found for biological systems, such that proteins are encoded by mRNAs
which are in turn encoded by pieces of DNA, and the law that for every natural
substance on this planet that can be broken down to yield free energy, there is
an organism that does precisely that.
On the basis of this experience, we expect that many more theories will be
established for living systems. These will differ from those we already know
