When discussing evolution it is necessary to make a clear distinction between macro-evolution and micro-evolution (see

10.5). Macro-evolution produces new species. This is Darwinian evolution. Micro-evolution, on the other hand, produces new ecotypes. Domestication is a form of agro-evolution, and it results from artificial selection, rather than natural selection. But it is also micro-evolution, and it produces agro-ecotypes (see 1.22).

The characteristics of cultivars, such as a high yield, and a high quality of crop product, are the result of artificial selection and domestication. They represent a maximisation of certain variables which, in the wild ecosystem, are present at their local optimum, rather than their maximum.

This maximisation of yield and quality is made at the expense of competitive ability in a wild ecosystem. Cultivars cannot survive in a wild ecosystem. Nor need they do so. They survive in an agro-ecosystem because farmers protect them from wild competition. And they compete within an agro-ecosystem by the maximisation of their yield, quality, resistance, etc.

There is no apparent reason why durable resistance should not be domesticated in a manner similar to that of yield, quality of crop product, and so on. This is necessary because epidemics tend to be more severe in crops than in wild ecosystems, because pure stands of very large, genetically uniform host populations are more conducive to epidemics. Furthermore, the quality control of parasite damage is economically important, in that consumers do not like grubs in salads and apples, or produce that is damaged in other ways.

The prospects of increasing the current levels of durable resistance in our cultivars are good. This is partly because we have been losing this kind resistance for most of the twentieth century, because of breeding for vertical resistance, or breeding under the protection of crop protection chemicals (see 6.6.1). But it is also due to the fact that we can domesticate resistance, just as we have domesticated other quantitative variables, such as yield and quality of crop product.

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