200
G. DETcHEv, and A. MOSKONA t
minImUm, whether it has feedbacks or not. The statement then appears
tautological and is equivalent to saying that a stable steady state is achieved. ~
My second difficulty arises from his statement that this minimum dissipation
of free energy shows "that an optimal aim really exists" and that he seems to
suggest that organisms are "basically different" from physical systems. Again,
if he simply means that organisms have many feedback interactions and therefore may, for example, have a smooth transient towards any steady state or
that they are therefore well buffered towards many perturbations, I have no
quarrel with the statement. I would not like to call such response characteristics an "optimal aim" but would consider it a somewhat dubious metaphor.
Dr. DETcHEv, however, seems to imply something more, namely, that organisms have evolved in response to an internally given criterion, a criterion
given by the thermodynamic and kinetic nature of self-regulating systems.
It is my view that organisms have evolved their present complex constitution
in reponse to externally set criteria, determined by natural selection, which has
existed for the whole life span of the species. The ultimate criterion is usually
described as the maximisation of fitness, which is broadly in terms of the number of viable offspring left by each generation. The elab~rate feedback mechanisms, at allleveis of organisation, are thought to "serve" this criterion insofar
as organisms lacking these, or having others, have been eliminated in competition with those we find now. Thermodynamic and kinetic relations appear to
place a constraint on evolutionary and organizational possibilities although they
also provide the basis for the realization of these possibilities. ~ The particular
"solution" which anyone species has come to is a function of its particular
evolutionary past and the particular ecological niche it now occupies. The
"control mechanisms" exhibited are therefore specific to each of these solutions and are, for example, very different for E. coli and man. Dr. DETCHEV
suggested that each species is at its own minimum. It is, of course, true that
each species is, by definition, the "best" for its niche, an observation made
many years ago by VOLTAIRE in his well known paper entitled "Candide".
DETCHEv:
The system studied by us is not a hypothetic one but rather constructed in
order to reflect the processes really occurring in biological objects. It takes
into consideration the existence of degrading as well as of conjugated reactions.
The minimum dissipation of energy~maintained through a balance between
these two kinds of reactions and thus representing, the optimum functional
of the system~is dependent on a set of feedbacks, exactly determined, and
on the interaction between their elements. Therefore, it is not possible to arbitrarily add any further feedback to the framework of the established system. In
various systems the n.umber of minimum effective feedbacks may be different;
this, however, is a question of the numerical solution on the basis of concrete
data and is without significance for the general handling of the problem. ~
The minimization of the dissipation of free energy should not be interpreted
as homeostasis. In the transition to a new steady-state~caused by any disturbance ~ the transition trajectory is simply determined by the optimum principle,
i.e. among all the possible trajectories the one is realized which energetically is
the most favorable one. ~ The existence of an optimum aim is not the result
of a minimum dissipation, but rather conversely the latter seems to be the consequence of the former. Thus, the availability of an optimum self regulatory
apparatus within living entities is the cause for the qualitative differences
existing between organisms and physical systems. As against Dr. KACSER'S
G. DETcHEv, and A. MOSKONA t
minImUm, whether it has feedbacks or not. The statement then appears
tautological and is equivalent to saying that a stable steady state is achieved. ~
My second difficulty arises from his statement that this minimum dissipation
of free energy shows "that an optimal aim really exists" and that he seems to
suggest that organisms are "basically different" from physical systems. Again,
if he simply means that organisms have many feedback interactions and therefore may, for example, have a smooth transient towards any steady state or
that they are therefore well buffered towards many perturbations, I have no
quarrel with the statement. I would not like to call such response characteristics an "optimal aim" but would consider it a somewhat dubious metaphor.
Dr. DETcHEv, however, seems to imply something more, namely, that organisms have evolved in response to an internally given criterion, a criterion
given by the thermodynamic and kinetic nature of self-regulating systems.
It is my view that organisms have evolved their present complex constitution
in reponse to externally set criteria, determined by natural selection, which has
existed for the whole life span of the species. The ultimate criterion is usually
described as the maximisation of fitness, which is broadly in terms of the number of viable offspring left by each generation. The elab~rate feedback mechanisms, at allleveis of organisation, are thought to "serve" this criterion insofar
as organisms lacking these, or having others, have been eliminated in competition with those we find now. Thermodynamic and kinetic relations appear to
place a constraint on evolutionary and organizational possibilities although they
also provide the basis for the realization of these possibilities. ~ The particular
"solution" which anyone species has come to is a function of its particular
evolutionary past and the particular ecological niche it now occupies. The
"control mechanisms" exhibited are therefore specific to each of these solutions and are, for example, very different for E. coli and man. Dr. DETCHEV
suggested that each species is at its own minimum. It is, of course, true that
each species is, by definition, the "best" for its niche, an observation made
many years ago by VOLTAIRE in his well known paper entitled "Candide".
DETCHEv:
The system studied by us is not a hypothetic one but rather constructed in
order to reflect the processes really occurring in biological objects. It takes
into consideration the existence of degrading as well as of conjugated reactions.
The minimum dissipation of energy~maintained through a balance between
these two kinds of reactions and thus representing, the optimum functional
of the system~is dependent on a set of feedbacks, exactly determined, and
on the interaction between their elements. Therefore, it is not possible to arbitrarily add any further feedback to the framework of the established system. In
various systems the n.umber of minimum effective feedbacks may be different;
this, however, is a question of the numerical solution on the basis of concrete
data and is without significance for the general handling of the problem. ~
The minimization of the dissipation of free energy should not be interpreted
as homeostasis. In the transition to a new steady-state~caused by any disturbance ~ the transition trajectory is simply determined by the optimum principle,
i.e. among all the possible trajectories the one is realized which energetically is
the most favorable one. ~ The existence of an optimum aim is not the result
of a minimum dissipation, but rather conversely the latter seems to be the consequence of the former. Thus, the availability of an optimum self regulatory
apparatus within living entities is the cause for the qualitative differences
existing between organisms and physical systems. As against Dr. KACSER'S