Macroevolution and Microevolution

There are six differences between macro-evolution and microevolution.

Macro-evolution is often called Darwinian evolution. Its definitive characters are:

  • It normally requires periods of geological time (i.e. millions of years).
  • It is evolution above the species level.
  • It produces changes that are new.
  • It is irreversible; macro-evolution never goes backwards.
  • It produces new species.
  • It leads to an increase in complexity.
  • It produces new genetic code.

Micro-evolution is the converse in all of these attributes:

  • It operates during periods of historical time.
  • It is evolution below the species level
  • It produces changes that are not intrinsically new.
  • It is reversible.
  • It produces ecotypes, agro-ecotypes, pathodemes, and pathotypes, but not new species.
  • It does not lead to an increase in complexity; it merely rearranges existing complexity.
  • It does not produce new genetic code.

The term 'evolutionary competition' usually refers to macro-evolution, while the term 'ecological competition' usually refers to micro-evolution. All day-to-day pathosystem considerations concern ecology and micro-evolution. When Johnston (1979) coined the much-quoted term 'man-made evolution', in connection with the breakdown of vertical resistance, he was, of course, referring to micro-evolution.

Because of agricultural misconceptions, it is often thought that the evolution of entirely new vertical genes can occur in historical time. This is believed to be true of vertical parasitism genes that ruin an otherwise valuable cultivar. It is often believed to be true of vertical resistance genes also. However, because these genes may be new to science does not mean that they are new to nature.

In fact, it is clear that the evolution of a gene-for-gene relationship requires macro-evolution. This is because the natural selection is operating on emergents, not on the effects of single genes. This macro-evolution can result only from group selection operating on emergents such as the n/2 model (see 4.15). Emergents such as these occur only at the higher systems levels and they involve the mutual survival advantage of groups of such distantly related organisms as plants and insects, or plants and fungi.

However, the functioning of a gene-for-gene relationship requires micro-evolution. It employs ecological mechanisms of homeostasis, such as density dependent selection, for the maintenance of pathosystem balance.

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