Biology Reference
In-Depth Information
Chapter 13
Mechanisms of the Origin of Life
13.1 The Anderson Model of the Origin
of Biological Information
Any theory purporting to account for life cannot avoid facing the fundamental
question about how life originated on this planet. One of the most physically
realistic models of the origin of biological information (and hence of life) that
I know of was proposed by P. W. Anderson and his coworkers (1983, 1987) (see
Fig.
13.1
). The model was based on thermal cycling (i.e., the cyclical changes of
the temperature on the surface of the earth due to its daily rotation around its axis)
of an RNA “soup” presumed to be present somewhere on the primordial earth
surface some 3.5 billion years ago. The following quotation from Anderson (1987)
describes the key ideas behind his model:
The autocatalytic mechanism which must be at the core of any prebiotic evolution
scheme is the complementary conjugation of polymeric molecules, nominally RNA. It is
assumed that the thermal cycle periodically breaks up the weak conjugation bonds between
RNA polymers, and at a later stage allows them to reconjugate randomly. Once two
polymers have simultaneously conjugated with the same 'template', matching adjoining
sequences (see the RNA double strands located on the bottom of Fig.
13.1
; my addition),
they are permitted with some probability to bond completely together, thus elongating
the chain and reproducing a longer sequence of the 'template'. This is the basic autocata-
lytic process, while the basic energy source is a constant supply of energy rich monomers
(or short sequences of 2 or 3 monomers) which are added at each cycle and can be joined to
the sequences already present by the conjugation-thermal cycling process. To achieve
realism and a reasonably steady state, we must also postulate an error probability and a
probability of chain death and/or breaking.
...
Anderson based his model of the origin of biological information on the concept
of “frustrations” imported from spin glass physics (van Hemmen 1983).
Frustrations
are observed in physical systems with three or more components,
each being able to exist in at least two energy (or spin) states (conveniently
designated as + and -, or up and down, with opposite signs attracting and identical
ones repelling each other) but, no matter how their spins are arranged, there exists at
