Biology Reference
In-Depth Information
molecular genetics became the mainstream approaches to cellular biology the
number of biologists using a more mechanistic approach to systems of molecules
was small. However, there always remained a group of mathematical biolo-
gists that continued to relate system properties to molecular properties through
quantitative methods and in fact this has become one of the roots of con-
temporary systems biology (Westerhoff & Palsson, 2004). The early examples
include: Turing, 1952; Hodgkin & Huxley, 1952; Chance et al., 1960; Goodwin,
1965; Glansdorff & Prigogine, 1971; Kauffman, 1971; Goldbeter & Lefever,
1972; Kacser & Burns, 1973; Heinrich & Rapoport, 1974; Rapoport et al., 1974;
Savageau, 1976; Atkinson, 1977; Reich & Selkov, 1981; Westerhoff & Van
Dam, 1987.
The unificationist and the mechanistic explanations are not unique to systems
biology; they are common to physics and chemistry as well. Yet, they are sus-
picious, for the unificationist type of explanation is alien to many biologists,
who see their discipline as just a large number of special cases. Of course
with the sequences of various genomes becoming known, the principle of unity
of biochemistry, discovered by Kluyver, is reinforced, and indeed in DNA
sequences the communalities are so strong that function can often be predicted
on the basis of sequence homology. Clearly there is much space for unifica-
tionist explanations in systems biology. The mechanistic explanation is spe-
cial as it is such an enormous challenge vis-à-vis the enormous complexity of
living cells.
3. OTHER TYPES OF EXPLANATION ARE ALSO IMPORTANT
FOR SYSTEMS BIOLOGY
A type of explanation that is hardly, if at all, accepted by molecular biologist is
the nomological explanation, where from a clearly defined set of premises certain
properties are derived. Examples abound in mathematics; the derivation of the
second law of thermodynamics through statistical mechanics is an example. In
systems biology (and one of its predecessors, metabolic control analysis (MCA)),
the summation and connectivity laws are examples (Kacser & Burns, 1973;
Heinrich & Rapoport, 1974; Westerhoff & Chen, 1984).
A type of explanation that is symmetrically unaccepted in physics but common
to biology is the design explanation (e.g. Wouters, 1999). Here phenomena are
explained by specifically referring to the advantage the presence of a certain item
or a certain kind of behavior has for the organism in comparison to its absence or
to another kind of behavior, respectively. In such explanations, answers to 'why'-
questions are given within the realm of functional biology. So, we disagree with
Mayr who claimed that giving answers to 'why'-questions is about evolutionary
