A. G. Cairns-Smith has proposed a mechanism by which evolution may produce
changes in the genetic substrate of organisms. His theory illuminates one
aspect of how today's high-technology mechanisms of heredity are most likely to
The idea is perhaps best explained by a diagram:
The large, yellow regions represent phenotypes.
G1 is the primary genetic substrate, and G2
is the secondary one.
Arrows within organisms indicate paths of genetic expression.
A simple organism with genetic substrate G1 produces substance
G2 as a component of its metabolic processes.
G2 is inherited - and comes to carry heritable information.
Gradually, G2 displaces G1 as the primary
genetic material for the organism.
Differing types of "phenotype construction" technology
The differing shapes of the phenotype regions in
the diagram above are intended to indicate that the second
genetic substrate may facilitate the construction of
qualitatively different types of phenotypic machinery,
compared to what is available from the original genetic
This effect may be responsible for driving the adoption of
the secondary genetic substrate - if this allows more
convonient access to superior phenotype-construction
The principle of genetic continuity
Before this mechanism was clearly elucidated, it was widely believed that the
principle of genetic continuity would rule out many types of dramatic
changes to the genotype. It seemed that any modification would require the old
genotype to still be readable by the new genetic machinery - in order to
maintain a continuous line of descent of viable organisms.
Consequently, it seemed likely that the original genetic material was related to
the modern genetic machinery such that the two could be linked by a series of
The mechanism of genetic takeover allows for the possibility that a secondary
genetic material can arise not as a modification of the primary one,
but rather from molecules synthesized under its control.
The possibility of genetic takeovers allows for extremely
dramatic changes in the genotype without violating pure Darwinian
gradualism. It consequently provides great freedom when considering what the
very first genetic substrate might have been.
The resulting liberation allowed Cairns-Smith to propose that the first living
organisms were in fact extremely different in their construction from
the type of organism we are now familiar with.
In fact, he proposed that our ultimate ancestors were actually
clay mineral crystals.
Regardless of whether his theory of crystalline ancestry is correct, it
still seems very likely that genetic takeovers were involved in the
origin of today's genetic machinery.
Evolution of the genetic substrate
A genetic takeover provides a clear scenario in which an organism
contains more than one type of heritable material.
Initially the second genetic material is not critical to the organism,
and may thus be subject to variation and natural selection - without changes
necessarily resulting in a non-viable organism.
A booster rocket
A cursory look at the diagram suggests that there is no mechanism for
information to be transferred between the two genetic substrates. The second
substrate has to "start from scratch" in coming to describe the organism.
A sceptic might suggest that this is just as difficult as the secondary genetic
material arising from scratch out of inorganic material - but this is not the
The secondary substrate can be a thermodynamically unlikely object, whose very
existence would be implausible in the absence of an existing evolutionary
process and natural selection. This alone means the primary genetic material is
In much the same way that a spaceship traveling into space requires a booster
rocket to get it out of the atmosphere, so early life required a boost from a
different mechanism to those which act as genetic machinery in modern organisms.
This is because the modern genetic mechanisms are too sophisticated to plausibly
form under pre biotic conditions.
In the same way that a spaceship discards its booster rocket as dead weight, so
the initial genetic machinery appears to have been completely discarded now that
a superior, high-technology alternative has been evolved.
While an immediate form of translation if the information present in
the primary genetic material to the language of the secondary material need not
exist, it is still possible for a significant quantity of information
to be transmitted across the divide between them.
The primary genotype is responsible for providing an environment in which the
second genome evolves.
Since the components in the original phenotype are replaced gradually,
approximately on a one-at-a-time basis, there is likely to be a functional
relationship between the original components and their replacements.
The Baldwin effect analogy
The information-transfer con be usefully compared to that which occurs with
the Baldwin effect. In the Baldwin effect, learned behaviors become
fixed genetically (over many generations). Information acquired by organisms in
the course of their lifetimes eventually finds its way into the gene pool.
With the Baldwin effect, the learned behavior creates an environment in which
genetic evolution (leading towards the organism displaying the learned behavior
instinctively) can occur more rapidly.
Similarly, in a genetic takeover, the primary genome creates an environment in
which evolution of the secondary genome can occur more rapidly in certain
There is another interesting analogy, with the process of endosymbiosis:
In endosymbiosis information can flow between the genomes of the organisms
involved, as they "compete" with one another to perform each other's
Unfortunately, horizontal gene transfer between endosymbionts and their hosts
can occur by the direct action of their DNA being physically mixed together,
partly obscuring the effect.
It appears that a likely result of endosymbiosis will be one of the participants
completely absorbing the functionality of the other, through a mixture of
horizontal gene transfer and copying of the supplied technologies.
It is important to emphasize the fact that there
can be ways to transfer information from the old
genetic medium to the new one - even if there is no specific
apparatus that can read the old medium and write to the new
Consequently, the idea that the new life is (genetically
speaking) the mortal enemy of the germ line of its ancestors
In a very real sense, some of the genetic information of the
ancestors can survive in their descendants.
The modern genetic takeovers
There have not been any significant changes to the genetic substrate for
billions of years.
However there are currently "various indications" that a
genetic takeover is imminent:
The rise of human culture
An examination of the communication of high-fidelity information between
organisms and their descendants reveals that almost all the information
transmitted over the history of life on earth has been via nucleic acids.
However very recently, various new methods of transmitting information
to descendants has arisen. These have the high-fidelity of replication
necessary to be able to support evolutionary processes, and are capable of
transmitting large volumes of information. These mechanisms are usually though
of as transmitting "cultural" information - but there is no fundamental
distinction between genetic information and cultural information in this
Until human beings came on the scene "cultural" transmission of information
existed - but was very limited in volume. For example, a bird's offspring may
inherit the songs of their parents - but probably only a small number of
generations will pass before it is not possible to identify the parents from the
songs of their descendants.
By contrast, human beings have brought with them the written word and - more
recently - books, CDs, DVDs and other optical, electro-magnetic and electronic
storage media. The result is a large volume of heritable, high-fidelity information
which is not transmitted through nucleic acids.
The ultimate effect of these types of new information storage media on
biological evolution could be extremely far-reaching.
Problems with the old medium
Nucleic acids are a form of molecular nanotechnology - as such they are a
compact, concise and surprisingly reliable form of information storage. It has
been sufficient to act as the primary information-storage medium for life for
the past four billion years.
However, currently, new storage media are frequently used in preference to DNA
for a number of reasons:
Today reading and writing information in nucleic acids
is a laborious rigmarole. Sequencing a single human genome
took years to complete.
Nucleic acids were "designed" to be replicated - but not
written to. Modern information storage demands the ability
to be easily modified when circumstances dictate this is
Nucleic acids are long, stringy
molecules. While it may be possible to grab them at
a specific point, they're not designed with this in mind.
They are like a tape - and lack the random access features
you would get with (say) a disc. in order to get at the
information you're looking for it is often necessary to do a lot of
fast-forwarding or rewinding.
Even copying a single nucleic acid chain is a tedious
and slow process. In principle it might be possible to break
it up and parallelise the process - but for rapid access to
the information, it is not currently an attractive option;
Only usable in a limited range of environments
Nucleic acid chemistry is effectively dependent on the
presence of liquid water, and a number of (admittedly fairly
common) organic compounds. There is no fundamental reason
why life should no exist at very low or high
Nucleic acids are essentially one-dimensional molecules. In
three dimensions they tend to coil up. Random access
considerations mean that future storage media are likely to
be two- and three-dimensional.
It's true that - in many respects, if you compare them to
DNA - most modern storage media appear to be sub-standard -
large, wasteful, and ugly.
However, having said this, nucleic acids are themselves a
hacked-together, evolved solution - which is more likely
to be a local optimum than an ideal method of information
storage for organisms.
It is virtually unthinkable that modern design and
technology will eventually fail to provide storage media
alternatives that are superior in almost every useful way to
Advantages of the new media
Human cultural information can be expressed in phenotypes in many diverse ways.
It can control the design of automobiles, or result in animated images or music.
Its volume can be very large, and it can be replicated with high fidelity.
Human culture is subject to conventional Darwinian evolution - but is also
subject to Lamarckian processes, and to intelligent design. These demand an
information-storage medium with an ability to write data conveniently.
Today's electromagnetic, magnetic and optical storage devices seem likely to be
replaced by nanotechnological devices - or possibly mechanisms based on individual
atoms in crystalline lattices.
There may well eventually be advantages to the new media in terms of stability,
expense, access speed and the ability to modify the information. Some of these
were not significant criteria when the current genetic machinery was selected,
but they are important in storage media today.
New phenotype technology
If the original genetic takeovers were driven by the ability to direct new
technologies (e.g. proteins), it seems likely that a modern genetic takeover
will be driven by the same type of effect.
DNA is currently only used to influence phenotypes by directly controlling the
synthesis of some twenty amino-acids. The resulting protein machinery is
very flexible and can direct a large number of other types of
Despite this, nature has failed to master some relatively simple and obvious
mechanical technologies - for example, notoriously nature makes very little use
of the wheel.
At the moment it appears that a whole raft of new technologies is driving the
adoption of new genetic materials.
Most programmable computers are currently constructed from specifications that are
not stored in DNA.
Also, DNA appears ill-placed to directly control the synthesis of the important
Fullerene molecules. If a single area of chemistry was to be nominated as
signaling the end of the DNA/protein era, I would nominate
Buckminsterfullerene, nanotubes - and their chemical relatives.
The significance of these molecules may be primarily structural - or
they may eventually come to play important information-processing roles. Either
way it appears that the relatives of diamond and graphite are likely to be
important components of the organisms of the future because of their unique
DNA is too limited in terms of its means of phenotypic
expression, and in its ability to offer random access and
read/write access to its data rapidly.
While it may persist for an extended period, its eventual
complete replacement appears likely.
Certainly the era of its virtual monopoly on heritable
information is already over.
Note that as far as I know, the possibility of a modern genetic takeover was
first suggested by the robot builder, Hans Moravec.
It appears that genetic takeovers are a fundamental - though currently
little-understood - aspect of the process of evolution.
The fact that the takeovers near the start of life are very distant from us has
obscured their significance as evolutionary events.
Whenever evolution develops new information-storage devices there will be an
immediate "pressure" for genetic information to migrate into them. This process
will continue for as long as superior information-storage technologies exist.
It seems likely that the next genetic takeover will not be the last.
The information storage aspect of the medium will probably become increasingly
abstracted from the replication mechanism, and from the phenotypic expression of
In the light of the fact that we may now be facing the first genetic takeover
for several billion years, some interest in the mechanism behind them would
appear to be appropriate.
For a page of references to Cairns-Smith's theories see here.
A second essay categorizes different types of genetic takeover.