Graham Cairns-Smith - Clay Hypothesis

In simplified form, this is the clay hypothesis: Clays form naturally from silicates in solution. Clay crystals, as other crystals, preserve their external formal arrangement as they grow, snap, and grow further. Clay crystal masses of a particular external form may happen to affect their environment in ways that affect their chances of further replication. For example, a 'stickier' clay crystal is more likely to silt a stream bed, creating an environment conducive to further sedimentation. It is conceivable that such effects could extend to the creation of flat areas likely to be exposed to air, dry, and turn to wind-borne dust, which could fall randomly in other streams. Thus—by simple, inorganic, physical processes—a selection environment might exist for the reproduction of clay crystals of the 'stickier' shape.

There follows a process of natural selection for clay crystals that trap certain forms of molecules to their surfaces (those that enhance their replication potential). Quite complex proto-organic molecules can be catalysed by the surface properties of silicates. The final step occurs when these complex molecules perform a 'Genetic Takeover' from their clay 'vehicle', becoming an independent locus of replication - an evolutionary moment that might be understood as the first exaptation.

Despite its frequent citation as a useful model of the kind of process that might have been involved in the prehistory of DNA, the 'clay hypothesis' of abiogenesis is not so popular, as with several other abiogenesis hypotheses. As it was current and fashionable at that time, Richard Dawkins used it as the example model of abiogenesis in his 1986 book The Blind Watchmaker.