The sociocultural theatre and the evolutionary play

The sociocultural theatre and the evolutionary play J ames Steele The new Centre for the Evolution of Cultural Diversity (CECD), supported by the Arts and Humanities Research Council, is a successor to the Centre for the Evolutionary Analysis of Cultural Behaviour (see AI 2000/2001). Here the director of the CECD outlines the theoretical frameworks within which the Centre operates and the main research themes that will be pursued over the next five years.

The sociocultural theatre and the evolutionary play J ames Steele The new Centre fo r the Evolution of Cultural Diversity (CECD), supported by the Arts and Humanities Research Council, is a successor to the Centre fo r the Evolutionary Analysis of Cultural Behaviour (s ee AI 2000/2 001).He re the director of the CECD outlines the theoretical fra meworks within which the Centre operates and the main research themes that will be pursued over the next fi ve years.

T he Arts & Humanities Research
Council is once again investing in evolutionary archaeology.The investment is not a trivial one.In 2001, the council fu nded a research centre -based at UCL, and with an out-station at Southampton -to work for five years on the evolutionary analysis of cultural behaviour.It was one of only eleven such national research centres funded in this way, and the only one to be led by archaeologists.Such was the suc cess of this centre that the AHRC has now decided to fu nd it for another five years of work.Only one other AHRC Research Cen tre has received such renewed investment.The renamed AHRC Centre for the Evolu tion of Cultural Diversity was inaugurated in January 2006, with a programme of activities that will keep its researchers extremely busy until Christmas 2010.It remains based at UCL, with its offices in the Institute of Archaeology, and I have been appointed as its director.

Evolutionary culture theory
The centre's new award confirms that evolutionary-culture theory is now firmly established in the research landscape of the arts and humanities.For many, how ever, the basis of the approach is still a mystery.We have set ourselves the chal lenge of clearing up any confusion, by allocating substantial effort to communi cation and outreach.
Our field encompasses genetics as a window on human population history, but it also involves the comparative study of human languages, social systems and material culture.Unifying all of these is a Darwinian approach to human agency and cultural diversity.An approach such as this fo cuses on the relationship between the evolution of gene frequencies and the evolution of distributions of cultural traits.The principle is very simple.Given some reasonable assumptions concerning human cognitive and social psychology (how we make choices and how we learn from others), and given some other (but also reasonable) assumptions about the stabil ity of cultural representations as they are transferred between individuals, we can then apply quantitative models of the evolution of cultural traditions that bear some similarity to the models used to make sense of biological diversity.
Beneath this umbrella, at least three main positions exist.1For human behav ioural ecologists, the relationship between genes and culture is tightly bound by the expectation that human cultural systems and social agency serve to maximize indi viduals' reproductive fi tness.Others are less convinced.Dual-inheritance theorists recognize that humans adopt efficient rules of thumb for social learning, espe cially regarding whom to imitate when one is uncertain about the relative advantages of any one among several alternatives.These rules-of-thumb usually work -that is, they provide us with a low-risk time efficient route to an optimal set of beliefs, attitudes and skills in an uncertain world.But things can go wrong: given such biases and propensities to adopt behaviour cop ied fr om others without a proper and full evaluation, ideas can spread even when they might prove to be harmful.Finally, evolutionary psychologists are less san guine still.They recognize that the human mind has evolved cognitive mechanisms to meet practical challenges and solve real world problems, but that these mecha nisms arose in very different contexts to those of the modern world.Such hard wired rules of thumb, however well they worked in the past, may sometimes now show up as limiting factors or unwelcome biases: culture is evolving too fa st, and our mental hardware cannot always keep up.
These three positions -human behav ioural ecology, dual-inheritance theory, and evolutionary psychology -are not fully reconcilable.Nonetheless, they have proved a fertile source of ideas and hypoth eses for scholars in a wide range of disci plines, each of whom is committed to a scientific understanding of human cul tural diversity.These scholars share an expectation both that human agency is governed by cognitive biases and decision rules that tend to increase reproductive fitness, certainly in our evolutionary past and possibly also even today; and that large-scale patterns of cultural diversity are the aggregated outcome of individuals expressing such biases and decision rules in their day-to-day activities.Group-level processes are of course also important, not 20 least for understanding the emergence of stable social institutions for collective action; their explanation in terms of indi vidual-level processes is a focus of much current work,2 as is the evolutionary psy chology of religion, seen as a social mech anism that is norm enforcing.3 Much of the first generation of work on this approach took place in the USA.Key studies in the 1980s by Cavalli-Sforza & Feldman4 and by Boyd & Richerson5 laid the groundwork for a mathematical model of cultural transmission and its dynamics.Evolutionary approaches in psychology have also been prominent in the USA, thanks partly to the Santa Barbara school;6 but a more moderate approach has also been prominent since the 1980s, and is seen in an influential body of work on social intelligence and on "theory of mind".7 New initiatives have also emerged in Europe to promote an integrated evolu tionary approach in the social sciences, including the Max Planck Institute for Evolutionary Anthropology in Germany (founded in 1997), and the Leverhulme Centre for Human Evolutionary Studies in Cambridge (founded in 2000).The McDon ald Institute for Archaeological Research in Cambridge has also been a forerunner in this fi eld.Our own AHRC Centre, with the benefit of Stephen Shennan's able leader ship in its first phase, has now become an established player and has been the source of many innovative applications of evolu tionary approaches in the fi eld of material culture studies.

New approaches to cultural diversity
What then, in practice, does an evolution ary approach to culture involve?One focus of our work has been on rates of inno vation, which is the source of cultural variation, analogous to mutation or recom bination (or both) in genetics.Bentley and eo-workers have studied distributions of traits in systems that are highly internally diverse and have high turnover ratesmodern baby names, contemporary chart pop music, prehistoric pottery design motifs -to identify dynamics consistent with a neutral model.8 This model, derived from genetics, assumes that neutral muta tions occur at a constant rate, and that the rates at which individual traits are propa gated (in cultural systems, through imita tion) vary random!y.A consequence of this is that the fr equency distribution of vari ants can be described by a power-law curve, whose coefficient (a measure of the concentration of abundance in a few vari ants) scales with the population size and the rate of innovation.Lake & Venti, mean while, have studied the evolution of diver sity in new technologies where variation is not neutral, using the well documented case of the history of bicycles.9 The pattern is one of initially high diversity, subse quently winnowed to leave a few success ful design solutions, each with its own A second focus of our work has been on the social interactions that provide the pathways for cultural transmission.One source of conservatism, or historical con tinuity in cultural patterns, is vertical transmission -the transfer of knowledge between generations, often from parents to offspring.Some time ago, Shennan and I found that craft skills in societies with a household mode of production tend to be transmitted in this way, and most often .

..1940 0 1944 01946 01946
between parent and offspring of the same sex.10At a larger scale, Collard, Tehrani, Jordan and eo-workers have been investi gating vertical transmission and cultural diversity in the ethnographic record.11 This investigation is facilitated when language differences between societies now in close geographical proximity reflect a migration event by one group in the relatively recent past.They find that some cultural similar ities reflect recent interactions among neighbours, but others must reflect more deep-rooted and conservative historical traditions -with the two patterns having different degrees of importance in differ ent aspects of craft design and technique (Fig. 1).
The counterpart to such vertical trans fers of knowledge is horizontal transmis-  Modern case studies help to explain the dynamics of cultural change, and the situ ations may have similarities to those seen in the archaeological record.In the middle of the twentieth century a higher-yielding hybrid strain of corn was developed and gradually adopted in the USA.The pattern of spatial diffusion (Fig. 2a) implies a dual inheritance explanation for farmer's adop tion decisions -i.e. a contagion-like spread influenced by proximity and by imitation of prior adapters.However, the scatter plot (Fig. Zb) suggests a rational-choice expla nation.Later-adopting states -which tend also to be those where agricultural produc tivity is lower, and where farm sizes are smaller -substituted the new strain for the older strains at a slower rate.Probable rea sons for this are that suppliers of the new strain preferentially targeted the Corn Belt states first; that the potential for increased yield was less apparent to farmers in the less productive regions; and that there was regional variation in the allocation of effort on selective breeding of hybrids adapted to local conditions by agricultural experi mental stations in different states.In this modern case, the process was very fastinstantaneous on an archaeological time scale -and there is no likelihood that demic diffusion can explain the spatial pattern.This process cannot therefore be compared with the Neolithic transition in Europe.However, in both cases, local vari ation in crop-growing conditions would have been an important factor influencing rates of spread.14 A third focus of our work is on devel oping rigorous comparative methods to identify cultural adaptations.We cannot simply record the frequency with which a particular cultural trait is associated with a particular feature of economy or environ ment, and then -if the associations occur often -assume that the cultural trait is adaptive.This is because some societies may occupy similar environments and have similar practices simply because, his torically, they are closely related.We want to be able to study many independent instances where historically closely related societies vary in their ecological and socioeconomic characteristics.If, in all or most such instances, the society that has adopted a new economic strategy "X" or responded to a new ecological challenge "Y" has done so by innovating a new cul tural solution " Z", then we can be confi dent that this is because such societies are converging on a single optimal solution that is, we are seeing cultural adaptation.
Holden & Mace have developed and applied this comparative method, con firming -in Bantoid-language pastoralists of sub-Saharan Africa -the adaptive sig nificance of the association that exists between cattle keeping and a switch from matriliny to a patrilineal or mixed pattern of descent and group membership.15 As part of this project, Holden has also gener ated a new language tree showing the prob able historical relationships among the languages in the Bantu family.16

New directions for the second phase
During the second phase of the Centre, work will continue in these areas, divided among three major themes.A new focus will be developed that cuts across all three of these themes on questions relevant to the Palaeolithic period, specifically, the evolution of spoken language and its rela tionship to the evolution of toolmaking and tool-using skills.17 Th eme A: Demographic processes and cultural change We shall examine the relationship between demographic factors (population size, structure, and stability), and cultural diversity.The relationship of population dispersals arising from sub sistence innovations with language-family expansions has been widely discussed in recent years, and models have also been proposed for the cultural significance of population decline.It is often suggested that, at least before the origin of states, the emergence of new adaptations that tend to support higher population densities and population expansions was the main basis for cultural macro-evolution.We shall examine such hypotheses and develop an analytical framework within which to test these, necessitating cooperation between ARCHAEOLOGY INTERNATIONAL archaeologists, anthropologists, geneticists and behavioural biologists.
Th eme B: Cultural and linguistic diver sity We shall examine the relationship of evolutionary change in linguistic systems to that in social practices and in material cultural traditions.Central to explaining how cultural diversity arises and how it is maintained is an understanding of the rela tionship between linguistic and cultural descent, the extent to which they are branching or reticulating, and the factors affecting their descent histories.Have cul tures always mixed and hybridized as they have come into contact with one another, or have groups maintained boundaries that insulate them strongly from outside influ ence, so that difference arises mainly when groups split and move apart?We shall continue to explore such issues, with col laboration between archaeologists, anthro pologists and historical linguists.
Th eme C: Innovations in complex social networks We shall examine the extent to which the growing scale and complexity of human social networks has changed the speed and the manner in which new cultural variation is generated.We shall examine spatial and network aspects of the diffusion of innovations at a general level, and we shall examine the effects of inter action patterns on innovation rates in pre industrial urban societies.This theme will enable the centre to involve archaeologists and anthropologists working on early state level societies.
The character of the phase 2 Centre will therefore be more interdisciplinary, and will involve geneticists, linguists and behavioural biologists, as well as archae ologists and anthropologists.It will also engage more actively with non-specialists and sceptics, to promote its work but also to identify the existing limits of the various approaches.These activities are only now getting under way, and we shall report on them, and on the Centre's continuing progress, on the CECD website and in future issues of Archaeology In ternational.18

JFigure 1
Figure 1 AHRC CECD post-doe famie Tehrani's PhD research investigated the evolution of material culture diversity in tribal populations of western Central Asia.He uses phyla genetic methods to analyze variations in textile-weaving techniques and motifs (such as the examples shown on the left} to reconstruct the descent of these gro ups' craft traditions fr om common ancestral assemblages (represented by the tree diagram on the righ t).(R eprinted fr om Tehrani & Collard, n. 11, fig.2, p. 449, reproduced with the permission of Elsevier.}

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taken to mean transfers among unrelated individuals of the same generation, but also including the larger scale geographical diffusion of ideas and practices.Work by Colledge, Conolly and eo-workers has focused on the transition to agriculture in Europe, tracking the spread of different strains of domesticated culti varsY Work by Gkiasta, Russell and eo workers had previously mapped the large scale chronology of the transition, and had addressed the problem of differentially diagnosing two local growth and dispersal processes -demic diffusion (dispersal of people) and cultural adoption (dispersal of ideas) -from the archaeology.13

Figure 2
Figure 2 (a) Diffu sion of hybrid corn usage, showing areas that planted ten or more per cent of their corn acreage to hybrid seed at successive time intervals (redrawn after Griliches 1960 ].(b) Wi thin-state rate of increase of hybrid corn use, plotted against the date of arrival in each state (the date at wh ich hybrid corn reached 10% of all corn).Data fr om Griliches (1 957) with revised growth coefficient estimates fr om Dixon (1 980; coefficient b2).From Steele (forthcoming; see n. 14).