Pathosystem Balance

The world is still green. This assertion can mean only that every wild plant pathosystem has very effective autonomous controls, which prevent either the parasite or the host from causing excessive damage, each to the other. It is clear that these controls can have evolved only by group selection. It is also clear that this group selection occurs at almost the highest of taxonomic levels because the 'group' consists of at least two different species, usually as evolutionarily remote from each other as plant hosts and either insect or fungal parasites. This is systems evolution. It represents natural selection operating on emergents, at the highest systems levels, in complex adaptive systems. It is in this context that the parallel evolution of the alternating parasites of plants (see 8) becomes so interesting. It is remarkable that parasites as evolutionarily remote from each other as insects and fungi should have evolved such complex yet fundamentally similar life cycles.

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