Nonetheless, the bare fact that von Neumann's model proved to be remarkably prescient does not in itself explain why, or in what circumstances, this genetic mode of reproduction will be useful or appropriate. Von Neumann himself proposed two reasons:
Both of these are, of course, directly applicable to natural, biological, reproduction, and they may well be adequate to explain the significance of genetic architecture in that case. However, the situation is different when considering the engineering of reproduction to support artificial evolution.
Even in von Neumann's own most detailed design of such a system (in his 29-state cellular automaton space, von Neumann 1953), the first reason above does not directly apply, because this space allows for essentially arbitrary configurations to be rendered into a ``quasi-quiescent'' state. The second reason--the dimensionality constraint--does apply to this system; it is effectively two dimensional and thus quite strictly limits inspection without disassembly to one dimensional structures. However, this is a self imposed restriction. In fact, if the entities of interest are embedded in some artificially engineered space then the ``dimensionality'' of interactions can be specified quite arbitrarily.
This can be seen very clearly in a number of recent model evolutionary systems, perhaps the best known of which is Tom Ray's Tierra (Ray, 1992). In this system, the evolutionary actors are small computer programs, inhabiting a shared random access memory or RAM. These are not constrained by either of the two problems identified above. The individual memory locations are quasi-quiescent in a similar sense to von Neumann's cellular model; and by the very nature of ``random access'' memory, any location can be inspected without disturbance and without constraint--the dimensionality of interaction is effectively unlimited.4 Because of this, arbitrary program entities in Tierra--from the simplest to the most complex--can be made to reproduce simply by copying of the program image in RAM--i.e., template based reproduction. That being the case, there is certainly no obvious reason to invoke the more involved mechanism of genetic reproduction; and, indeed, in the experiments reported by Ray and his co-workers, only template style reproduction has been used.
However, notwithstanding this, we now wish to draw attention to one further distinction between template and genetic style reproduction--which may still mean that the latter is preferable even in artificial systems where von Neumann's original reasons for proposing it need not apply.
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