Monday, 14 November 2016

Cultural evolution vs cultural epidemiology

Jason Collins recently raised the issue of cultural evolution vs cultural epidemiology, thus:

Then there is the question of whether evolution is the right framework for all the forms of cultural transmission? Are models for the spread of disease a better fit? You will find plenty of discussions of this type of question across the cultural evolution literature, but little convergence.

I think it's fair to say this issue has been widely discussed - with some folks promoting "viruses of the mind" and "cultural virus theory" for example, and other folk criticizing them. However the issue is not very complicated and should not be that controversial. Here's a position summary that I think that most knowledgeable parties should be able to agree on:

Models of disease spread often need to be generalized before being applied to culture. One issue is the sign of the fitness correlation between symbiont and host. Diseases almost always have a negative fitness correlation with their hosts - i.e they reduce host fitness. By contrast, culture can have positive or negative effects on host fitness. The sign of the fitness impact matters, since negative fitness impacts on hosts are resisted and rejected, while positive fitness impacts on hosts are promoted and encouraged. Symbiology performs this generalization. However symbiology generally deals with close relationships. There's a larger field that deals with all kinds of relationships - known as biological interactions. Models of biological interactions are highly suitable for modeling cultural evolution.

Many models of epidemiology are explicitly evolutionary these days. It is widely recognized that parasites evolve in real time - including within host lifetimes. Less widely recognized, but still well-established science is the notion that host immune systems use evolution and natural selection to adapt to the parasites they face. Evolutionary epidemiology is clearly a thing. The main cases where non-evolutionary models of epidemiology are useful is when dealing with short time scales - or highly simplified models. For example, fleas might spread through an island community without either them or their hosts evolving very much. A similar cultural example of where a non-evolutionary epidemiological model might be appropriate is where Rubik cubes spread through a network of children in schools. Here, neither the cubes nor the children are doing much change or evolution. As a first approximation, models based on evolutionary theory can be ignored in favor of simple epidemiological models.

It is certainly true that in cultural evolution, epidemiological models are sometimes the most appropriate. The exact same thing is true in the organic realm. However evolutionary and epidemiological models are generally complementary and compatible - they are best used under different circumstances.

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