Tuesday, March 4, 2008

Natural selection and culture

A paper was published this week in PNAS on rates of culture change and has an interesting commentary by Stephen Schennan. As its open access you can get it here.

Here's the basics on the paper:

Natural selection and cultural rates of change

Deborah S. Rogers and Paul R. Ehrlich*

Department of Biological Sciences, Gilbert Building, 371 Serra Mall, Stanford University, Stanford, CA 94305

Contributed by Paul R. Ehrlich, December 17, 2007 (received for review November 5, 2007)

It has been claimed that a meaningful theory of cultural evolution is not possible because human beliefs and behaviors do not follow predictable patterns. However, theoretical models of cultural transmission and observations of the development of societies suggest that patterns in cultural evolution do occur. Here, we analyze whether two sets of related cultural traits, one tested against the environment and the other not, evolve at different rates in the same populations. Using functional and symbolic design features for Polynesian canoes, we show that natural selection apparently slows the evolution of functional structures, whereas symbolic designs differentiate more rapidly. This finding indicates that cultural change, like genetic evolution, can follow theoretically derived patterns.


I like papers that suggest that we shouldn't just assume that certain features of culture are immune to scientific inquiry.

Cultural evolution is one of those areas of anthropology/social science with lots of baggage - both in terms of misguided criticisms and in terms of misused analytical techniques and models - but its an area that is rapidly growing and seems to consistently make provocative findings - as this paper does.

So they study boats from Polynesia:
"Finding cultural traits with which to test such ideas proved difficult. The traits we settled on were the design elements of canoe building across Polynesian societies. We have since learned that the French philosopher Alain (Émile-Auguste Chartier) in 1908 proposed that boat design would be subject to natural selection (26). "Tout bateau est copié sur un autre bateau... Raisonnons là-dessus à la manière de Darwin. Il est clair qu'un bateau très mal fait s'en ira par le fond après une ou deux campagnes, et ainsi ne sera jamais copié... On peut donc dire, en toute rigueur, que c'est la mer elle-même qui façonne les bateaux, choisit ceux qui conviennent et détruit les autres" (pp 41–42). [Every boat is copied from another boat... Let's reason as follows in the manner of Darwin. It is clear that a very badly made boat will end up at the bottom after one or two voyages, and thus never be copied... One could then say, with complete rigor, that it is the sea herself who fashions the boats, choosing those which function and destroying the others. (Translated by D.S.R.)]"

They divide traits of the canoes into those that seem likely to directly impact the canoe's performance (functional or design characteristics) from those that do not (stylistic), so you need to be comfortable with that dichotomy.

that state: "Our expectation was that the functional traits would change at a significantly different rate from that of symbolic traits."

They statistically evaluated what the differences in rates of change were between the stylistic and functional groups across the islands through time. The statistical technique was interesting - they compared a randomized assignments of functional vs. stylistic to a Wilcoxon signed rank frequency distribution for the recalculated Jaccard distances. I don't know if there were better ways to conduct this test or not. They found that the rates were different, with functional traits changing at a slower rate.

They conclude that: 1) such evolutionary perspectives are indeed good for the study of culture change (a rah rah team conclusion); 2) this identifies the different mechanisms that might act on culture change, and; 3) design features don't change randomly or 'mutations' indicating the link between canoe design and actual survival characteristics. Changes must be conservative and thought out... etc.


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