The Origin of Life - Criticism
Most of the criticisms of Crystalline Ancestry
I have encountered are not very substantial.
A lack of evidence is often mentioned as the barrier to
It's true that more studies would be welcomed - and that
more research would probably help with this - but I think
that there is enough evidence available now for competent
individuals to evaluate the theory.
Many seem to object to the idea of a
genetic takeover as being
unparsimonious - or contrary to Occam's razor.
Others ridicule the idea of unreactive silicon elements
being the basis of life - when carbon chemistry offers such
I've also encountered the criticism that Cairns-Smith is a reductionist thinker - an "Ultra-Darwinian" far more extreme than (say) Richard Dawkins. This may have some truth to it - but reductionism is great. The "charge" of using reductionism should not adversely affect the assessment of scientific theories - rather it is a positive thing.
Two pages of "The Fifth Miracle" are devoted to Cairns-
Smith's ideas (p. 116-117).
The ideas are summarised, with the comment:
It has to be said that there is very little
experimental evidence to support Cairns-Smith's clay theory.
Still, whatever the plausibility of clay as the primal life
stuff, the basic principle of genetic takeover is sound.
J. Maynard Smith
J. Maynard Smith's give the theory a cursory treatment in The Major
Transitions in Evolution. He says:
Maybe - but it seems to me that heredity has been much
more convincingly demonstrated than with any
prebiotically-plausible organic materials.
Heredity has not been convincingly demonstrated.
At least clay enthusiasts can show that information is being
copied with enough accuracy to preserve it many thousands of
times, in an inorganic process.
Christopher Wills and Jeffrey Bada
Two pages of "The Spark of Life" are devoted to Cairns-
Smith's ideas (p. 101-102). The authors add:
These criticisms are silly, and betray a lack of familiarity
with the ideas involved.
Unfortunately for his idea, it quickly became
apparent that minerals simply could not carry enough
information to be the genetic material for even the most
primitive life. This mineral-first hypothesis also faces
another severe problem: If clays were the bases of life, why
aren't traces of them still inside us? [...]
Cairns-Smith's notions about clay genes have now been
largely rejected by the scientific community. [...]
Stephen C. Meyer
Stephen C. Meyer has some critical comments
Alas, they hardly seem worth criticising.
No evidence indicates that a "low tech" clay-life ever
existed or was transformed into organic-based substances.
More importantly, like the primordial soup approach, the
theory does not account for the so-called "information
problem" of genetics.
This is where Cairns-Smith's theory breaks down. He hopes to
someday prove that what he terms his clay "crystal genes"
can store information. He offers no clues, however, as to
how either "high tech" amino acids or "low tech" clay
crystals might have arranged themselves into complex
biochemical messages. In the absence of any mechanisms
explaining these mysteries. Cairns-Smith invokes the
literary device, to bridge the gap, of endowing evolution
with attributes of intelligence. The "machinery of life," he
says, was built from "well-chosen components" with "an
entire design approach" and a "cleverness that could only
have been a product of evolution."
I have a separate page of Criticism of Shapiro's ideas.
John A Hewitt
John A Hewitt discusses Cairns-Smith's idea
Unfortunately, he shows no awareness of what Cairns-Smith's idea actually was.
The Scottish chemist Cairns-Smith (1971) suggested that
prebiosis occurred in defect structures on silicate (rocky)
surfaces and this idea has been quite widely support since
some such rocks, notably the clay montmorillonite, exhibit a
wide range of catalytic activities. The feeling is that
these surfaces might help to solve the problem of bounding
by keeping reagents together, especially if lipids were also
John Horgan, "In the Beginning," Scientific American, February 1991, 264(2), pp107-108.
For more than a decade, Cairns-Smith has been pushing his
own hypothesis. Like Wachtershauser, he proposes that life
arose on a solid substrate that occurs in vents and almost
everywhere else, but he prefers crystalline clays to pyrite.
All crystals consist of self-replicating units, Cairns-Smith
points out, but clay crystals have enough complexity to
mutate and evolve in a lifelike way. Some clays might have
become still better breeders by developing the ability to
attract or synthesize organic compounds-such as nucleic
acids or proteins. Eventually, the organic compounds would
become sophisticated enough to begin replicating and
evolving on their own.
Unlike some origin-of-life theorists,
Cairns-Smith cheerfully admits the failings of his pet
hypothesis: no one has been able to coax clay into something
resembling evolution in a laboratory; nor has anyone found
anything resembling a clay-based organism in nature. Yet he
argues that no theory requiring organic compounds to
organize and replicate without assistance is likely to fare
any better. "Organic molecules are too wiggly to work," he
Did Cairns-Smith really say 'wiggly'?
The usual turn of phrase in this context is that
"organic molecules are usually too sticky" to self-assemble.
Leslie E. Orgel
[Origin of Life on Earth by Leslie E. Orgel]
Some 30 years ago he proposed that the very first
replicating system was inorganic. He envisaged
irregularities in the structure of a clay - for example, an
irregular distribution of cations (positively charged ions)
- as the repository of genetic information. Replication
would be achieved in this example if any given arrangement
of the cations in a preformed layer of clay directed the
synthesis of a new layer with an almost identical
distribution of cations. Selection could be achieved if the
distribution of cations in a layer determined how
efficiently that layer would be copied.
So far no one has tested this daring hypothesis in the
laboratory. On theoretical grounds, however, it seems
implausible. Structural irregularities in clay that were
complicated enough to set the stage for the emergence of RNA
probably would not be amenable to accurate self-
Wikipedia's article on Silicon-based life contains:
Life as we know it could not have developed based on a
silicon biochemistry. The main reason for this fact is that
life on Earth depends on the carbon cycle: autotrophic
entities use carbon dioxide to synthesize organic compounds
with carbon, which is then used as food by heterotrophic
entities, which produce energy and carbon dioxide from these
compounds. If carbon was to be replaced with silicon, there
would be a need for a silicon cycle. However, silicon
dioxide precipitates in aqueous systems, and cannot be
transported among living beings by common biological
As such, another solvent would be necessary to sustain
silicon-based life forms; it would be difficult (if not
impossible) to find another common compound with the unusual
properties of water which make it an ideal solvent for
This criticism is illogical and incoherent. Silicon-based
life can work in water without any particular difficulty.
The fact that silicates precipitate in water is not a
Mark A. S. McMenamin
[The Garden of Ediacara]
Cairns-Smith felt that there must have been some sort of
inorganic scaffolding on which the earliest life would have
started. He proposed clay as the living crystal of Gene-1.
More recent research has shown that clay does not have the
properties needed to act as the scaffolding of Gene-2.
The claim that clay "does not have the properties needed to
act as the scaffolding of Gene-2" is unreferenced and
Cairns-Smith gets some rough justice at the hands of one
[here] (now archived here).
Again, it is hard to take Massimo very seriously - since he
doesn't seem to know what he is talking about.
A contemporary discussion of the question of the origin of
life cannot be complete without the inclusion of A.G.
Cairns-Smith's theory of clay crystals. I hope this will not
be the case for much longer (except as a footnote of
historical value). Don't get me wrong, I am familiar with
Cairns-Smith's research and writing, and I find it
excellent. But everybody can make a mistake, and I think the
clay theory clearly falls within the cracks of Cairns-
Smith's career, as ingenious and superficially enticing as
it may be.
Briefly, the idea is that life didn't originate with either
nucleic acids or proteins. The original replicators and
catalyzing agents were actually crystals found everywhere in
the clay that lay around the primitive Earth. There are four
cardinal points of Cairn-Smiths hypothesis. First, crystals
are structurally much simpler than any biologically relevant
organic molecule. Second, crystals grow and reproduce (i.e.,
they can break because of mechanical forces, and each
resulting part continues to "grow"). Third, crystals carry
information and this information can be modified. A crystal
is a highly regular structure, which tends to propagate
itself (therefore, it carries information). Furthermore, the
crystal can incorporate impurities while it's growing. These
impurities alter the crystal's structure and can be
"inherited" when the original piece breaks (hence, the
information can be modified). Fourth, crystals have some
minimum capacity of catalyzing (i.e., accelerating) chemical
Cairns-Smith then proposed that these very primitive
"organisms" started incorporating short polypeptides
(protoproteins) found in the environment - presumably in the
soup - because they enhanced the crystals' catalyzing
abilities. The road was suddenly open for an increase in the
importance of proteins first, and then eventually of nucleic
acids, until these two late arrivals on the evolutionary
scene completely supplanted their "low-tech" progenitor, and
gave origin to the living organisms that we know today.
What is wrong with this picture? First of all, Cairns-Smith
seems to completely ignore what a living organism is to
begin with. For one thing, crystals don't really have a
metabolism, not in the sense defined above for living
organisms. The reason for this may have something to do with
the fact that not only are crystals structurally much less
complex than a protein or a nucleic acid, but also with
their silicon-based chemistry, recognizably much simpler
than the carbon-based chemistry utilized by living organisms
on Earth. The lower complexity and simpler chemistry may be
insurmountable "hardware" obstacles to the origination of a
true metabolism in clay matter. Second, crystals don't
really react to their environment either, another hallmark
of every known living creature. Notice that this is a
property distinct from metabolism, in that metabolism can be
entirely internal, with no reference to the outside world
(except for some flux of energy that must come into the
organism to maintain its metabolism). On the other hand,
living organisms universally and actively respond to changes
in external conditions, for example by seeking sources of
energy or by avoiding dangers. Furthermore, an argument can
be made that crystals are not actually capable of
incorporating new information in their inherited "code,"
unlike what happens with mutations in living beings. True,
they can assimilate impurities from the environment and
"transmit" such "information" to their "descendants" for
some time; but these impurities do not get replicated, they
need continually to be imported from the outside, and they
do not become a permanent and heritable part of the crystal.
Moreover, impurities do not create new types of crystals,
the way mutations give rise to entirely new kinds of animals
Another colossal hole in the clay theory is - of course -
that we have no clue to how the "mutiny" of nucleic acids
and proteins actually occurred, and in fact we are given
very faint hints about how a crystal could possibly co-opt a
polypeptide to enhance its growth. Therefore, as much as
creationists might like the flavor of a theory of the origin
of life in which the first living beings came literally from
dust (although Cairns-Smith is certainly no creationist),
we're still left with ribonucleo-proteins as our best,
albeit fuzzy, option.
Lastly, apparently A. G. Cairns-Smith is reported dead (in 2006):
Um, he might have something to say about that!
1968 - A.G. Cairns-Smith publishes a paper suggesting that the
first life on earth might have been fine-grained clay
crystals. He will publish on this topic several more times
before his death, but the experimental evidence will remain
scant, perhaps in part because sufficient technology doesn't
yet exist to test the hypothesis.
Most of the critics I've encountered would be well-advised
to actually read "Genetic Takeover".