Thursday, 29 October 2015

An ensemble of evolutionary theories

Various folk have expressed concern that a generalized version of Darwinism that covers more phenomena would be weaker and would constrain expectations less - and would therefore be less useful.

John Maynard Smith once wrote:

The explanatory power of evolutionary theory rests largely on three assumptions: that mutation is non-adaptive, that acquired characters are not inherited, and that inheritance is Mendelian - that is, it is atomic, and we inherit the atoms, or genes, equally from our two parents, and from no one else. In the cultural analogy, none of these things is true. This must severely limit the ability of a theory of cultural inheritance to say what can happen and, more importantly, what cannot happen.

Recently, Alberto Acerbi has expressed a similar concern:

I am not convinced by the way-too-easy claims of “everything evolves!”, such as here, mainly because it seems to me that broad conceptions of evolution tend to have less explicative power

I've previously replied to Maynard Smith, writing:

Let's assume for a moment that his conclusion is true - and that it is harder to make predictions with cultural evolution than it is with biological evolution. So what? Theories of cultural evolution are not in competition with theories of biological evolution - they compete with other theories of cultural change that are less inspired by Darwinism.

Here I want to offer a different response - which is nonetheless still based on the idea that theories that cover different domains are not direct competitors.

Darwinism can be axiomatized. The axioms can be weakened and/or discarded, resulting in cut-down versions of Darwinism that apply under different circumstances. For example, conventionally, Darwinism requires copying. However without copying you can still have selection and goodness of fit - which are important components of Darwinism. Another common constraint involves what counts as a mutation. Random mutations constrain expectations a lot and result in easily falsifiable theories. However under some circumstances, such a constraint on mutation is not realistic. In cultural evolution, for example, it can be quite reasonable to model mental mutations as consisting of practically any change (short of recombination) that can happen inside an individual's mind. Mutations are still relatively small - but since they are the result of multiple generations of copying and selection within an individual's mind, they can be adaptive. Other Darwinian axioms can also be usefully weakened.

However, the resulting broad theories aren't in direct competition with the earlier narrow ones. They are applicable in different domains. As a result we have an ensemble of more-or-less Darwinian evolutionary theories - which are applicable under different circumstances. Having these extra theories in no way weakens the old, narrow versions of Darwinism from the textbooks. Those still work just as they did before. However the new, broader theories extend evolution into new realms, such as physics, chemistry, geology, astronomy and computer science.

Here's a diagram of the ensemble of evolutionary theories:

Theories vary along a one-dimension axis from 'specific' to 'general'. The more general theories are vaguer and constrain expectations less. However their corresponding advantage is that they are still applicable in application domains where narrower theories fail completely.

The expanded domain of evolutionary theory represented by universal Darwinism is like having a bunch of new tools in your toolbox. The complaints of John Maynard Smith and Alberto Acerbi are a bit like complaints that some of the new tools aren't as useful as one of the old tools was. That's OK - these are new tools that we didn't have before. You don't have to throw out any of your old tools in order to make room for the new ones. Instead, take delight in all the new things the bigger toolbox lets you do.

Of course this doesn't address the terminological debate about what deserves to be described as being 'evolutionary' or 'Darwinian'. However that's more of a 'small peanuts' debate, in my humble opinion. Universal Darwinism gives us a bunch of shiny new tools. We should try them out, see what they can do, and learn when best to use them.

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