Monday, 9 June 2014

Mark Ridley's definition of "Evolution"

Mark Ridley's "Evolution" textbook excluded three forms of change from its definition of "evolution". These were:

  • Changes during development;
  • Ecosystem changes not affecting gene frequencies within species;
  • Cultural changes.

Excluding cultural changes is obviously contrary to the spirit of this blog - but I have come to realize that these other exclusions are equally invalid. Changes during development count as evolutionary - most obviously the development of the immune system and individual learning are conventional Darwinian evolutionary processes. Lastly, I think that ecosystem changes should count as evolution too. It is true that some define evolution to be changes in relative gene frequencies. However, in practice it really matters whether your population size is two or two million.

Part of the motivation for excluding such processes from evolutionary theory appears to have been to help make evolution a scientific theory, capable of being refuted. If all change is classified as being evolutionary, then no observations can refute the concept - and the term "evolution" becomes a redundant synonym.

However, it seems to me that there is a better candidate for the role of making evolution a testable concept: the requirement that evolution be consistent with physical law - that it proceed without miracles.

Excluding cultural change, developmental change and ecosystem-level changes from the evolutionary process unnecessarily victimizes and diminishes those processes. Evolution ought to be defined in a manner consistent with Occam's razor. A laundry list of excluded topics is not appropriate.

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