news
projects
publications
resources
people
search
contact
 
news archive
events
members
What is the CECD? 
The CECD is an AHRC funded research group dedicated to examining the evolutionary underpinnings of human cultural behaviour, past and present. more>

   
Page Title - projects
Phase 2: Theme B - Cultural and linguistic diversity: Project B003
The Evolution of Cultural Diversity in Iranian Tribal Populations: Core Traditions or Multiple Lineages?

SUPERVISOR: - Shennan, Collard

Jamshid Tehrani (Anthropology, Durham University)
Stephen Shennan (Institute of Archaeology, University College London)
Mark Collard (Department of Archaeology, Simon Fraser University)

PROJECT FUNDING: Cards Against Humanity
fridge freezers

PROJECT ABSTRACT:
The project will address a long-standing problem in the anthropology of Iran, which relates to the origins and maintenance of cultural diversity among tribal groups in the country. In his classic ethnography Nomads of South Persia (1961) Frederik Barth observed that there are two principal mechanisms that operate in the growth and multiplication of tribal units, which he termed ‘segmentation’ and ‘aggregation’. Segmentation occurs when a herding group or lineage splits into two new groups. Aggregation, on the other hand, occurs when two declining groups join forces, or when one group is assimilated by another. Segmentation and aggregation correspond to two contrasting models of cultural evolution: In ‘phylogenesis’ new cultural assemblages arise from ancestral ones through branching processes of descent, whereas in ‘ethnogenesis’ cultural assemblages evolve through borrowing and blending among contemporaneous traditions. Although most anthropologists have assumed that cultural evolution is dominated by ethnogenesis, recent empirical work suggests that phylogenetic splitting processes might be a lot more important than was previously thought.

To shed more light on these issues, a series of analyses will be carried out using data on material culture and linguistic variation among Iranian tribal groups. First, a cladistic analysis of material culture traits will investigate how far similarities among the techniques and designs used by different tribes fit a phylogenetic, tree-like model of descent. A second analysis will assess how well patterns of material culture inheritance fit an independently derived phylogeny based on linguistic data and ethnohistorical information on tribal origins. The purpose of this comparison will be to shed more light on the relationship between patterns of cultural evolution and the sort of demographic processes which Barth identified as important influences on these groups’ population histories. As several researchers have pointed out, understanding this relationship is essential to the correct interpretation of cultural phylogenies. Here, two possibilities will be investigated: In the first scenario, the craft practices and languages associated with Iranian tribal groups form part of a set of ‘core traditions’ which are transmitted as a single unit of inheritance from ancestral populations to descendent ones and evolve in a strongly tree-like fashion. According to this scenario, we would expect a strong consensus among the material culture phylogeny, the language phylogeny and ethnohistorical data. The second scenario, on the other hand, allows for the possibility that language, material culture and other traditions represent distinct packages of inheritance which evolve in a tree-like way but which may have be rooted in different ancestral sources. Consequently, patterns of cultural descent among Iranian tribal groups cannot be described by a single phylogeny because they comprise ‘multiple lineages’. Thus, according to this scenario, languages and material culture phylogenies may conflict with each other and with ethnohistorical data on population histories. Although researchers in the field of cultural phylogenetics have long considered the ‘core traditions’ and ‘multiple lineages’ hypotheses to be equally plausible, this will be one of the first case studies to directly test the predictions of both models.



FINAL PROJECT REPORT:
During phase 2 of the Centre I carried out just over a year's research into the project, B003-The Evolution of Cultural Diversity in Iranian Tribal Populations: Core Traditions or Multiple Lineages? Although I left CECD to take up a post at Durham University I met all the projected outputs and outcomes associated with the project, some of which were completed subsequent to my departure.

I carried out several analyses that were designed to address the fundamental questions of this project: How did patterns of material culture diversity among Iranian tribal populations evolve? To what extent can the history of these groups craft traditions be linked to patterns of linguistic inheritance? I addressed these questions in relation to two models of cultural evolution. In the first model, the craft practices and languages associated with Iranian tribal groups form part of a set of 'core traditions' that are transmitted as a single unit of inheritance from ancestral populations to descendent ones and evolve in a strongly tree-like fashion. According to this model, we would expect a strong consensus among the material culture phylogeny, the language phylogeny and ethnohistorical data. The second model proposes that there may not be a single cultural core but 'multiple packages' of inheritance that may originate in different ancestral sources. Thus, according to this model, languages and material culture phylogenies may conflict with each other and with ethnohistorical data on population histories.

To test these models I firstly carried out a cladistic analysis of 150 craft traits to reconstruct the historical relationships among different tribes' weaving traditions. The results of the analysis suggested that these relationships were consistent with a tree-like model of common descent. The second stage of the investigation involved reconstructing a linguistic family tree using previously published data on the classifications of the various Turkic and Farsi dialects spoken by the tribes. The third stage of the investigation examined how far patterns of material culture variation were consistent with patterns of linguistic differentiation. This assessment was made on the basis of two analyses. First, I used the Maddison and Slatkin test to establish whether the language tree fitted the craft traits data significantly better than randomly generated trees. The result suggested that there is evidence of historical associations between language histories and craft histories among Iranian tribal groups, but found that the fit was far from perfect. Therefore, a further analysis was carried out to explore how differences between the topologies in the craft tree and language tree may have arisen. The analysis employed a method that was originally developed to study historical associations between the lineages of host species and parasite species. The advantage of the method is that it is able to recover different types of processes, such as co-speciation and host-switching, which have clear parellels in cultural evolution (e.g. co-divergence of languages and cultural traditions resulting from populations splitting versus the horizontal transfer of cultural traditions across ethno-linguistic lineages). The results suggested that although the diversification of material culture traditions usually coincided with the bifurcation of linguistic lineages, there are also cases where craft traditions appear to have split within a single branch of the language tree or to have jumped across branches. These findings are therefore more compatible with the 'multiple packages' model of cultural evolution than the 'core traditions' model.

These findings shed new light on the evolution of weaving in Iranian tribal populations and made methodological advances in cultural phylogenetics that we hope will have a significant impact on the field.

ASSOCIATED PUBLICATIONS:
Matthews, L., Tehrani, J.J., Jordan, F., Collard, M. Nunn, C (2011).
Testing for Divergent Transmission Histories among Cultural Characters: A Study Using Bayesian Phylogenetic Methods and Iranian Tribal Textile Data. PloS One. Vol 6(4):e14810.
Tehrani, J.J., Collard, M. & Shennan, S.J (2010).
The cophylogeny of populations and cultures: reconstructing the evolution of Iranian tribal craft traditions using trees and jungles.. Philosophical Transactions of the Royal Society (B). Vol 365:3865-74.
Tehrani, J and M. Collard (2009).
The evolution of material culture diversity among Iranian tribal populations. In: S. J. Shennan (ed.) (ed\s) Pattern and Process in Cultural Evolution. University of California Press. 99-112.
Tehrani, J. and M. Collard (2009).
On the relationship between inter-individual cultural transmission and population-level cultural diversity: a case study of weaving in Iranian tribal populations. Evolution and Human Behavior. Vol 30(4):286-300.
Tehrani, J (2007).
The coevolution of craft traditions and ethno-linguistic groups in rural Iran. EHBES 2007 Conference.