HeritabilityA large number of experiments would throw more light on the clay theory.
The most obvious thing that needs doing is to demonstrate that information can be transmitted through a sequence of clay replicators. This is clearly possible when the layers of the clay are still joined together - but it that the information can be transmitted reliably when the crystals break is less well demonstrated.
I suggest the use of crystals with a acicular (needle-like) habitat - i.e. long thin crystals rather than short, flat ones.
If the crystals are fixed at one end, breaks are more likely to arise at the point where they are fixed - and - for a number of reasons, these breaks are less likely to result in a good site for new growth from the existing template.
I suggest attempting to use a "free fall" environment for the crystals - one where they are not liable to attach to the walls of the container too much.
Selecting for cross-section shapePossibly the most important way in which the cross section of a crystal could affect its chance of being copied is by using its surface to attract organic molecules. These undergo chemical reatcions with other attracted compounds nearby on the surface, influence the surface properties of the clay, and change factors such as its viscosity - and tendency to flocculate.
However, for the sake of simplicity, I've tried to think of a selection criterion which doesn't depend on the presence of organics.
Inclined planeA device that might be capable of creating crystals with a specific cross-sectional shape is a crystaliser on an inclined plane.
Selection for large crystals is an important reason for using an inclined plane.
Seeking large crystals should make detection easier. It should also mean that the most successful organisms are likely to exhibit a non-trivial phenotype.
The water should be allowed to move down the slope (rather than remaning fixed (e.g in a pipe). The crystals should be kept in constant motion by the motion of the water.
The incline should probably be relatively shallow. Too much of a slope and either the water will generate a lot of turbulence as it flows - or the larger crystals will wind up falling at some speed through the water, causing them to be more likely to dissolve again.
There are two main possibilities for selection on such a slope:
I'm inclined to think that selecting for rapid motion is the most attractive option.
AdaptationAssuming crystals can be persuaded to form rolling rods there are still two hypotheses that could explain the effect. One is evolution - but the other is that the crystal has had its rough edges knocked off by the process of being rolled - much the same process that can make grains of sand round.
Distinguishing between these possibilities may prove to be challenging.
Showing that the resulting entities roll better that other crystals (which had not been subject to selection for rapid motion) would not be sufficient - since round grains of sand are likely to roll faster than square ones - and yet are not the product of natural selection.
Showing that the crystals are closely related would show inheritance, though:
Natural selection would produce a small number of species - each with a characteristic size.
Frictional forces would produce a more continuous range of sizes.
This difference should allow the hypothesis of natural selection to be confirmed or rejected.