Monday, July 28, 2014

Lithics in Clairvaux and Chalain

An Approximate Bayesian Computation approach for inferring patterns of cultural evolutionary change Journal of Archaeological Science (Crema, E.R, Edinborough, K., Kerig, T, Shennan, S.J., 2014)

This paper builds on a  methodology for explaining cultural changes in the archaeological record.  It takes a data set spanning a time period (arrowheads in this case) and uses Bayesian modeling to try and explain the underlying behavior or factors behind those changes.

Pointe de Fleche, France [Iron]

The essential question here is about discontinuity in the archaeological record within the context of Cultural Inheritance or Cultural Learning Theory.  Human culture is not inborn, so when lithics, pots or sustainment strategies change in the archaeological record, either these new habits involved biased decision making or unbiased 'sponge' acculturation via some mechanism, say migration by unbiased adherents.

As a road test, the authors use data from the lithic transition phase in Southeastern France and crunch the numbers to predict why changes took place here 4,500 years ago near the emergence of the Beaker period.

As far as data goes, arrowheads offer data crunchers a good set of numbers because it is likely that most able-bodied men in these cultures made arrowheads (learned behavior).
Theoretically, lithic production would offer better data over pottery since it is something learned early with universal male participation.

So there are three scenarios that are offered by the authors here as a way of keeping things simple:

-Conformist Bias, individuals copy cultural attributes they perceive to be "mainstream".  In this scenario, native Neolithic peoples may copy what they consider to be "normal", not necessarily better for their personal sustainment.  They may have come to view their own villages as backwards subcultures, out of the mainstream.

-Anti-Conformist Bias, individuals copy what they consider "prestigious".  Again probably native Neolithic peoples imitating a cultural "elite" they deem superior (Beaker), again, not because the arrowheads are better but with some perceived benefit.

-Unbiased Transmission, this is basically osmosis.  This is probably what we would call a thoughtless, sponge-like acculturation.  A boy learns from his father or uncle how to make an arrowhead and doesn't question it. Migration would probably offer the best fit in lithic changes in this scenario.

One solution not offered is Direct Bias in which Beaker arrowheads are demonstrably superior on a technical level and which improves the survivability of individuals.  This could be wrench in the whole equation since barbed arrowheads are functionally better and are thought to accompany a period of military escalation in Western Europe.

The authors conclude that unbiased or anti-conformist bias could reach equifinality.  To put it bluntly (in my own understanding), both migration and the spread of an elite culture could explain lithic changes in Southeastern France and achieve the same result - Beaker Culture.

I'm not quite sold on this just yet.  Changes in weaponry, deeper defenses and deforestation in the Late Neolithic may make the details of arrowhead production more complex than our assumptions allow.

I like the concept but I would package clusters of cultural attributes to see where the various units are in agreement.  If within Beaker culture we have cultural changes that permeate all aspects of life through all periods of development, then when it is graphed it should tell us something fairly clear.
A wide range of theories and methods inspired from evolutionary biology have
recently been used to investigate temporal changes in the frequency of archaeological
material. Here we follow this research agenda and present a novel approach based on
Approximate Bayesian Computation (ABC), which enables the evaluation of multiple
competing evolutionary models formulated as computer simulations. This approach
offers the opportunity to: 1) flexibly integrate archaeological biases derived from
sampling and time averaging; 2) estimate model parameters in a probabilistic fashion,
taking into account both prior knowledge and empirical data; and 3) shift from an
hypothesis-testing to a model selection approach. We applied ABC to a
chronologically fine-grained Western European Neolithic armature assemblage,
comparing three possible candidate models of evolutionary change: 1) unbiased
transmission; 2) conformist bias; and 3) anti-conformist bias. Results showed that
unbiased and anti-conformist transmission models provide equally good explanatory
models for the observed data, suggesting high levels of equifinality. We also
examined whether the appearance of the Bell Beaker culture was correlated with
marked changes in the frequency of different armature types. Comparisons between
the empirical data and expectations generated from the simulation model did not show
any evidence in support of this hypothesis and instead indicated lower than expected
dissimilarity between assemblages dated before and after the emergence of the Bell
Beaker culture.
doi: 10.1016/j.jas.2014.07.014

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