Introduction

Parasitism is often regarded as being competition between host and parasite. This view is probably an error, and it is highly doubtful that parasitism is ever competition between host and parasite, at any systems level, and on any time scale. It would be equally misleading to think of parasitism being co-operation between host and parasite, although much pathosystem behaviour might suggest this. Parasitism should be regarded as biological order, resulting from a remarkably effective self-organisation. This is self-evident from the successful co-existence of host and parasite over periods of geological time. That is, the parasite never impairs the evolutionary or ecological survival of the host. And the host never impairs the evolutionary or ecological survival of the parasite.

The evolution of a functioning gene-for-gene relationship, and a system of biological locking, cannot be explained on the basis of natural selection operating on random mutations (see 2.10). Indeed, any attempt at such an explanation leads to a reductio ad absurdum. But the evolution of such a system is easily explained on a basis of Kauffman's (1993) concept of natural selection operating on self-organisation within a complex, adaptive system. Indeed, the system of locking produced by the gene-for-gene relationship is itself an elegant example of biological self-organisation. It is also an elegant example of biological order, and it is an excellent example of an emergent. Its evolution can perhaps be explained best in terms of natural selection operating on emergents.

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