As discussed by Robin Torrence (1986: 5), exchange is not directly observable but requires interpretation of the evidence found in consumption sites and in the initial procurement and production areas for artifacts.
Figure 2-4. Model for inference about prehistoric exchange (from Torrence 1986: 5).
Seldom does the act of exchange leave direct evidence of having occurred in a particular location, and the activity must be inferred from the circumstances surrounding production, exchange, and consumption of the product. Note that "Acquisition" (Figure 2-4), or the source area for a product, links directly to all other modes except discard and re-use. In other words, as observed by Torrence, quarry areas are in a unique position for investigating a complete exchange system because it is only "Acquisition" at the quarry area that articulates in some form with most of the major nodes in the Figure 2-4 conceptual model.
When archaeologists encounter non-local materials in their studies, there are commonly three alternative interpretations for this evidence of contact: (1) migration, (2) trade or exchange, (3) conquest by a non-local group. Differentiating these forms of contact from archaeological consumption data can be difficult, and a larger view of the context of exchange is required.
In the 1970s when exchange studies were being widely discussed by archaeologists, two principal approaches were adopted: (1) The system-level view, presented by Renfrew and his associates (1969;1972;1975), and, (2) the political or social view of trade relations (Adams 1974;Friedman and Rowlands 1978;Kohl 1975;Tourtellot and Sabloff 1972) that became more prominent in the 1980s. The systems-oriented approach integrates data into a comprehensive framework, but it is weakened by gradualistic and adaptationist underpinnings as it is
...assumed to have a smoothly, internal inevitability of its own... however it is absurd to think of this as the path that at least the more complex societies have normally followed. They dominate the weaker neighbors, coalesce, suffer themselves from varying forms and degrees of predation, develop and break off patterns of symbiosis - all in dizzyingly abrupt shifts (Adams 1974: 249).
As more recent, agent-centered analyses argue, exchange is a dimension of society that is particularly susceptible to the ambitions of entrepreneurs or aspiring elites because expressions of non-local association and alliance are one manner in which social differentiation can be achieved (Appadurai 1986:38;Clark and Blake 1994;Wiessner 2002: 233).
Anthropological accounts relate that acquiring resources through trade with neighbors is sometimes a dangerous undertaking that is maybe not far removed from raiding and warfare. "There is a link, a continuity, between hostile relations and the provision of reciprocal prestations. Exchanges are peacefully resolved wars, and wars are the result of unsuccessful transactions" (Lévi-Strauss 1969: 67). Further, Sahlins (1972) observes that reciprocity in trade between unrelated exchange partners in contexts without overarching political control can be a very delicate affair because sometimes it is only the perception of fairness in the exchange that maintains peace.
When people meet who owe each other nothing yet presume to gain from each other something, peace of trade is the great uncertainty. In the absence of external guarantees, as of a Sovereign Power, peace must be otherwise secured: by extension of sociable relations to foreigners - thus, the trade-friendship or trade-kinship - and, most significantly, by the terms of the exchange itself (Sahlins 1972: 302, emphasis in the original).
Yet exchange and markets across boundary areas are common features in world history. Such exchange could consist of "border mechanisms" with trade-partnerships or fictive-kin ties that permit "interactions across tribal boundaries under conditions of peace and personal security" (Harding 1967: 165). Zones between social groups are particularly likely to have active trade and markets if there is some cultural or ecological variation between the groups, such that the products circulating in each zone complement one another (Hodder and Orton 1976: 76). The No-man's-land described as the "Intertribal sector" by Sahlins (1965;1972: 196-204) is a good locale for such exchange because complementary products are available for exchange, and because the morality of exchange in neutral geographical territories permits balanced or negative reciprocity between traders. In perception of value, as well as geography, these border zones can be conceived as overlapping social "spheres of interaction" as described by Barth, where "entrepreneurs will direct their activity preeminently towards those points in an economic system where the discrepancies of evaluation are greatest, and will attempt to construct bridging transactions which can exploit those discrepancies" (Barth 1967: 171). These discussions of the details and great the variability in entrepreneurial strategy anticipate the challenges of an agent-based approach to ancient trade (Adams 1974: 243;Hodder 1982).
The question of the isolation of producers and traders from consumers also connects theories about exchange with the issue of the physical form of the exchange goods. Archaeologists investigating the role of stone artifacts in prehistoric economies observe that lithic manufacture is a subtractive technology as stone artifacts always get smaller with use and maintenance. The degree of reduction of stone material at a lithic source determines the kinds of forms that subsequent artifacts will take.
Jonathon Ericson (1984) applies Sahlins' concept of a continuum of social distance in exchange relationships, discussed above, to the directional, reductive nature of lithic production systems. He explores the idea that the degree of lithic reduction that may occur could be reduced when social distance increases because the producer would have less information about the consumer and the end forms that material will take (Ericson 1984: 6). For example, if the procurer does not know if the nodule will be formed into bifacial lancoleate knife or a triangular projectile point by the consumer, it would be better to leave the nodule in a larger form.
Exchange partners can be slow to respond to changes in the needs of consumers in a given exchange system (Ericson 1984: 6;Harding 1967;Rappaport 1967;Spence 1982), and the effects of social distance can impact production, exchange, or consumption patterns. The implications of social distance for lithic reduction are that, as a subtractive process, reduction circumscribes the potential artifact forms that a nodule of raw material may take in the future. Countering this tendency, people can reduce risk in tool production by producing blanks closer to the source of a raw material where the value of a material is lessened and the costliness of knapping error or breakage, and inconsistent or poor-quality material, is reduced. Stylistically, producers may wish to impart a local motif to the material; alternately, in order to maximize distributive potential, a good may be left in a minimally reduced form.
Non-local exchange goods are prominent in anthropological models of socio-political change because exchange goods can accrue value directly as a function of scarcity, labor input, or through social and symbolic reference. As discussed above under the subject of practical goods and prestige goods, a given object may move between practical and prestige categories in different places, times, and social contexts. The availability of an item in a given milieu communicates not only the relative scarcity but, for alienable goods, the exchange value of that item; such items may also contain allusions to distant regions, social groups, and esoteric knowledge.
Theoretical models assert that in order for sacredness or exotic power to be conferred through possession of non-local goods, those goods cannot be widely available or mutable in economic circles accessible to just anyone (Clark and Blake 1994;Goldstein 2000). The possession and circulation of these goods have also been considered as part of a network strategy, distinct from a corporate strategy, towards acquiring influence and leadership (Blanton, et al. 1996). These goods may have served as indicators of long-distance association for trade and alliance, and also have served as a means of differentiation during this time of incipient political competition. In another approach, one that focuses on differential reproductive success, Craig and Aldenderfer (in press) use costly-signaling theory in a formal, biological adaptationist framework to model the development of social inequalities through the differential use of obsidian in southern Peru at the Archaic and Formative transition. Exotic materials have been used to demarcate commonplace from supernatural referents, or are at least part of a constellation of behavior and objects that signal status difference.
A pattern noted frequently by archaeologists is that close to the source of a raw material there is no distinction associated with the commodity as the item is abundant, whereas farther from the source, where access is intermittent, the possession of such commodities may acquire greater symbolic importance (Knapp 1990: 161;Renfrew 1986). It follows that if one moves from a place where a product is scarce and found in ritual contexts, towards the source of that product such that it becomes less scarce, one may observe a reduction in ritual or exclusive association for that group of goods. This theme will be considered with obsidian use in the Lake Titicaca region.
Furthermore, what of those who transport exotic goods? Mary Helms argues that "we should consider long-distance travelers or contact agents as political-religious specialists, and include them in the company of shamans, priests, and priestly chiefs and kings as political-ideological experts or 'heroes' who contact cosmically distant realms and obtain politically and ideologically useful materials therefrom" (1992: 159). These agents are in a position to benefit, in an entrepreneurial way from the value difference, between the source and the consumption zone, but in many cultural contexts their participation and social roles appear to be circumscribed. The association of non-local goods with status or prestige, long-distance alliance or esoteric knowledge is contingent on a variety of factors upon which it is difficult to generalize, but one can examine these archaeologically through artifact form and context.