Thursday, 17 October 2013

Universal Darwinism and the definition of life

When I was a child I learned in science class that distinguishing living systems from flames and crystals using a definition was hard, and that the best approach was to use a 'MR GRENS' definition - an acronym which defined life as involving: Movement, Respiration, Growth, Reproduction, Excretion, Nutrition, and Sensation. As a fairly intelligent child, this definition was not very satisfying.

Later in life I learned about evolutionary theory. It became clear that life was what evolved. I found this idea had been codified by J. Maynard Smith and Eors Szathmary - in "The Origins of Life", p.3:

What is life? [...]

An alternative is to define as living any population of entities possessing those properties that are needed if the population is to evolve by natural selection.

Still later I learned about Universal Darwinism, and the project of Darwinizing physics. The principles of Darwinian evolution were not confined to biology. They applied to inorganic systems - propagating cracks, electrical discharges, turbulence, drainage systems, etc.

At this point it became clear that the Maynard Smith / Szathmary conception of living systems had some issues. Either practically everything was alive, or this definition of life was in need of a rethink.

The latter option seems much more attractive than attempting to change the meaning of a common concept.

I think the concept of systems that exhibit cumulative adaptive evolution is more appropriate as a definition of life. Evolution by natural selection just isn't enough to pin the concept on life-as-we-know-it.

One problem with this idea is that it arguably includes structures such as drainage basins - which evolve adaptively over extended periods. For would classify drainage basins as being "alive". This definition may not be perfect - but it seems like a step forwards. At least cumulative adaptive evolution excludes many cases of degenerative Darwinism.

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