Biology Reference
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thermodynamic requirements for self-maintenance. From a physically realistic
perspective, a NTSMS cannot have appeared unless there exists a set of condi-
tions ensuring both the adequate concentrations of its fundamental components
and a specific order among their constitutive reactions (endergonic reactions
have to be adequately coupled with exergonic ones). As F. Harold has pointed
out (2001, p. 251) 'a credible biopoietic theory will be one that generates mount-
ing levels of complexity naturally, by providing the means to convert the flux
of energy into organization'.
Given the deep interdependence between the degree of complexity of an orga-
nization and its capacity for developing real self-maintenance, it is hard to imag-
ine the early steps of the process. In the absence of self-generated mechanisms
for maintaining the conditions of functioning, the earlier SMSs were probably
fragile or/and dependent on highly specific external conditions. A good example
is the hypothetical protometabolism proposed by G. Wächstershäuser (1988).
This author argues that certain mineral surfaces could have created the adequate
conditions for the appearance of a kind of what he considers a protometabolic
organization. He defends that the first 'surface metabolic network' was estab-
lished on the interface of solid/liquid phase (mineral surface/water). Under these
conditions the system could 'act' on the environment only establishing a buffer-
ing of pH or bringing down the tendency towards hydrolysis in its surroundings.
Other authors (Harold, 1986, Morowitz, 1992, Deamer, 1997, Segré et al., 2001),
however, consider very unlikely the possibility of a metabolic organization,
however primitive it may be, in the absence of any enclosure. Such scenario
would imply the necessity to elaborate models that integrate metabolism and
compartmentation simultaneously (Penny, 2005).
Be it as it may, it is likely that the earlier SM systems were highly dependent
on a set of external conditions upon which they did have few (if any) control.
Thus, their degree of robustness would be seriously restricted, and the accessible
level of complexity would also be low. In consequence, the appearance of NTSM
systems is linked to crossing a frontier between those organizations whose
identity was more dependent on a set of external conditions (let us call them
'predominantly passive SM systems') and those whose maintenance depends
more on their own organization (let us call them 'predominantly active SM
systems'). This frontier is precisely what defines the
autonomy
of the system.
4. NTSM ORGANIZATION AND AUTONOMY
The question of whether the earlier NTSMSs appeared in certain mineral sur-
faces, enclosed in primitive compartments or otherwise, is an empirical issue.
However, what in any case is essential is that the organization of the primitive
NTSMSs could control the external constraints necessary for their maintenance.
