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.

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.