A. G. Cairns-Smith - references to his work in popular science

A. G. Cairns-Smith - references

Richard Dawkins

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):

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 role.

[...]

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 van.

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

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 takeover:

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 complete. [...]

Daniel Dennett

”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

Robert Shapiro

Leslie Orgel

Paul Davies

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.

John Casti

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

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.

Misc

To quote:

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 once more.