A. G. Cairns-Smith - references to his work in popular science
A. G. Cairns-Smith - references
Cairns-Smith's ideas were favourably mentioned in Richard Dawkins' "The Selfish
The original replicators may have been a related kind of molecule to
DNA, or they may have been totally different. In the latter case we
might say that their survival machines must have been seized at a
later stage by DNA. If so, the original replicators were utterly
destroyed, for no trace of them remains in modern survival machines.
Along these lines, A. G. Cairns-Smith has made the intriguing
suggestion that our ancestors, the first replicators, may have
been not organic molecules at all, but inorganic
crystals-minerals, little bits of clay.''
- Richard Dawkins, The Selfish Gene, page 21.
...and in greater depth in
Chapter 6 of "
The Blind Watchmaker", 1982 (where the modern takeover gets mentioned):
Dawkins also speculates about dams and dust:
Cairns-Smith believes that the original life on this planet was based on
self-replicating inorganic crystals such as silicates. If this is true, organic
replicators, and eventually DNA, must later have taken over or usurped the
Cultural evolution is many orders of magnitude faster than DNA-based evolution,
which sets one even more to thinking of the idea of 'takeover'. And if a new
kind of replicator takeover is beginning, it is conceivable that it will take
off so far as to leave its parent DNA (and its grandparent clay if Cairns-Smith
is right) far behind. If so, we may be sure that computers will be in the
Dawkins describes this speculation as one of his "little flights of fancy" -
but somehow or another, this unlikely "dust" scenario has made it onto the
Cairns-Smith wikipedia page.
To speculate a little further, suppose that a variant of a clay improves its
own chances of being deposited, by damming up streams. This is an inadvertent
consequence of the peculiar defect structure of the clay. In any stream in
which this kind of clay exists, large, stagnant shallow pools form above dams,
and the main flow of water is diverted into a new course. In these still pools,
more of the same kind of clay is laid down. A succession of such shallow
pools proliferates along the length of any stream that happens to be
‘infected’ by seeding crystals of this kind of clay. Now, because the main
flow of the stream is diverted, during the dry season the shallow pools tend
to dry up. The clay dries and cracks in the sun, and the top layers are blown
off as dust. Each dust particle inherits the characteristic defect structure
of the parent clay that did the damming, the structure that gave it its
damming properties. By analogy with the genetic information raining down on
the canal from my willow tree, we could say that the dust carries
‘instructions’ for how to dam streams and eventually make more dust. The dust
spreads far and wide in the wind, and there is a good chance that some
particles of it will happen to land in another stream, hitherto not ‘infected’
with the seeds of this kind of dam-making clay. Once infected by the right
sort of dust, a new stream starts to grow crystals of dam-making clay, and the
whole depositing, damming, drying, eroding cycle begins again.
Hans Moravec used "genetic takeover" as the theme of his presentation at the
first "Artificial Life" conference:
Human Culture - A Genetic Takeover Underway, in 1987 - drawing attention to the
similarity between historical genetic takeovers and the one likely to be
precipitated by human cultural evolution.
In his 1988 book "Mind Children", pages 3 and 4 are devoted to Cairns-Smith's
theories - and their connection with the possibility of a modern genetic
Today, billions of years later, another change is under way
in how information passes from generation to generation.
Humans evolved from organisms defined almost totally by
their organic genes. We now rely additionally on a vast and
rapidly growing corpus of cultural information generated and
stored outside our genes - in our nervous systems,
libraries, and, most recently, computers.
Our culture still depends utterly on biological human
beings, but with each passing year our machines, a major
product of the culture, assume a greater role in its
maintenance and continued growth. Sooner or later our
machines will become knowledgeable enough to handle their
own maintenance, reproduction and self-improvement without
help. When this happens the new genetic takeover will be
Daniel Dennett gives Cairns-Smith a positive write-up in "Darwin’s Dangerous Idea":
”Nucleotides are too expensive” (Cairns-Smith 1985…). DNA exhibits too much design work to be a mere product of chance, Cairns-Smith argues, but then he proceeds to deduce an ingenious – if speculative and controversial – account of how that work might have been done. Whether or not Cairns-Smith’s theory is eventually confirmed, it is well worth sharing because it so perfectly instantiates the fundamental Darwinian strategy.
A good Darwinian faced yet again with the problem of finding a needle in a haystack of Design Space, would cast about for a still simpler form of replicator that could somehow serve as a temporary scaffolding to hold the protein parts or nucleotide bases in place until the whole protein or macro could get assembled. Wondrous to say, there is a candidate with just the right properties, and more wondrous still, it is just what the Bible ordered: clay!
Cairns-Smith shows that in addition to the carbon-based self-replicating crystals of DNA and RNA, there are also much simpler (he calls them “low-tech”) silicon-based self-replicating crystals, and these silicates, as they are called, could themselves be the product of an evolutionary process. They form the ultra-fine particles of clay, of the sort that builds up just outside the strong currents and turbulent eddies in streams, and the individual crystals differ subtly at the level of molecular structure in ways that they pass on when they “seed” the processes of crystallization that achieve their self-replication.
Cairns-Smith develops intricate arguments to show how fragments of protein and RNA, which would be naturally attracted to the surfaces of these crystals like so many fleas, could eventually come to be used by the silicate crystals as “tools” in furthering their own replication processes.
According to the hypothesis (which, like all really fertile ideas, has many neighboring variations, any one of which might prove to be the eventual winner), the building blocks of life began their careers as quasi-parasites of sorts, clinging to replicating clay particles and growing in complexity in the furtherance of the “needs” of the clay particles until they reached a point where they could fend for themselves…..”
Vernor Vinge mentions Cairns-Smith's work in the context of a modern "genetic takeover"
Robert Shapiro's "Origins" (Bantam 1986) discusses Cairns-Smith's ideas.
Leslie E. Orgel mentions Cairns-Smith's ideas
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.
There's a seven-page section in Paradigms Lost
devoted to Cairns-Smith's ideas:
John Casti revisits the theme of Cairns-Smith's clay theory
in Paradigms Regained.
Cairns-Smith says that carbon is much
too high tech a material for this job, and has offered a
fascinating silicon-based alternative with the claim that,
just as the Bible says, life started as a mere mote of dust
in someone's eye.
Maynard-Smith and Szathmary
Cairns-Smith's theory gets a page devoted to it in
The Major Transitions of Evolution, where it
is summarised and rejected, as follows:
Such problems [with prebiotic RNA synthesis] have led
Cairns-Smith (1971) to suggest that primordial genes or
were made not of RNA but of clay. This biblical idea is
not entirely unreasonable. Clay crystals are readily
formed from a saturated solution of the necessary ions.
They grow around crystal nuclei, and, once grown may fall
into several pieces, each piece being able to grow again.
But can such a system undergo evolution?
It is clear that clay crystals can multiply, but the
question of heredity is harder to answer. A crystal
through errors in the lattice, can store information. If,
and only if, the pattern of errors is replicated can we
speak of heredity. It is also possible to imagine
circumstances in which different crystals could be
differently selected. Imagine a porous sandstone into
which the saturated solution is leaking. From this, clay
begins to crystallise. Crystals with different errors might
grow at different speeds.
Crystals that are too loose might be easily washed away:
those that are too dense might block further percolation
of the saturated solution. It is therefore conceivable the
clay crystals could have hereditary variation that
affected fitness. If so, They could be units at evolution.
If for the moment we accept this conclusion, why and how
were clay genes replaced by RNA genes? The why is easy to
answer with hindsight: molecular information storage and
retreival is far more efficient. The how can be imagined
only gradually, in small steps. Some organic compounds can
be bound by clay minerals, and some of them may enhance
crystal growth. If clay genes had been able to manipulate
their organic environment, then sooner or later the
synthesis of RNA could also have become feasible. At first,
RNA it may have acted to stabilize the clay.
The main attraction of the idea lies in the difficulty in
explaining how RNA could have arisen spontaneously. In
Cairns-Smith's analogy, if we see an arch, we are tempted
to think that someone constructed a scaffold first, used
it to build the arch, and then removed the scaffold.
The arch is the RNA: the scaffold is the clay. However, a
good scaffold should be such that it can be constructed on
its own, and should be able to carry the weight of the
stones of the arch.
Unfortunately, there is no strong evidence that clay
minerals satisfy either criterion. Hereditary has not been
convincingly demonstrated. Even if clay minerals are able
to evolve, it is not guaranteed that they could have
reached the complexity of an RNA 'breeder'. It seems
better therefore to seek more conventional ideas about
what the scaffold may have been made of.
Here is a [book review of "Seven Clues"].
I cannot resist drawing an analogy here, by pointing to a loop which may be
about to rejoin its starting point: just as the evolution of inorganic
substances served (in Cairns-Smith's view) as a template for a switch to organic
evolution, so the organic species homo sapiens may serve as a template for the
establishment of a much more soaring evolutionary trajectory than the one we are
on. The inorganics, in the form of intelligent machines, look like taking over
Tim Tyler |