Down-the-line exchange can account for many archaeological distributions of cultural goods such as obsidian, both in volume and in temporal persistence. In terms of efficiency, down-the-line reciprocity networks require lower travel distance and less risk than is incurred traveling through unfamiliar territory (Renfrew 1975: 44). Furthermore, as Nielsen (2000: 24, 514) notes, caravan driving is hard work and it only becomes worthwhile when distances are large and/or loads are heavy or bulky. These bulky items tend to be transported medium distances (40-120 km), but smaller and more valued items might be transported long distances (Nielsen 2000). Traveling peddlers also carry small and light items without the added responsibility of managing many camelids in a caravan, therefore in some ways caravans and peddlers are complementary alternatives for the independent circulation of goods. Nielsen further observes that ancient caravans probably carried a variety of products in their cargo to reduce risk, and they likely carried anythingthat was worth transporting and that could be traded within their social and cultural parameters.

Given the evidence for increased sedentism from the Terminal Archaic and onwards (Aldenderfer 1998;Craig 2005), down-the-line exchange may be considered as the null hypothesis, with direct procurement and household level trade caravans as alternative hypotheses. Consistent but low levels of down-the-line exchange embedded in social relations form the background against which to examine other exchange modes such as caravans and possible non-market mercantilism. What kinds of possible incentives existed for the development of household-level caravans in order to acquire such goods, given the wide variety of potential trade and consumption patterns in prehistory? Incentives for household level caravan organization may include

(1) The maintenance of a social network and a demonstration of extra-local alliances that exceed the level of basic regional interaction implicated in subsistence-related exchange.

(2) Demand for a greater quantity of types, and the number or sizes of products than can be acquired from down the line exchange.

(3) A need or desire to exceed the products available to one's neighbors or to avoid dependency on an entire reciprocity network of neighborly relations.

(4) In a biological adaptationist framework, the risk and potential of caravan driving was a form of costly signaling (Aldenderfer 2006;Craig and Aldenderfer In Press).

Secure evidence of caravan activity, beyond simple evidence of pastoralism from faunal remains and evidence of corrals, may be a challenge for archaeologists and the systematic study of spatial distributions of non-local goods may shed light on the differences between subsistence pastoralism and caravan trade activity. One example of caravan activity from consumption contexts may come in the form of distinctive evidence of pooling of certain goods at particular sites along major transportation corridors, but establishing changes in relative density probably requires representative samples from archaeological collections from contexts that were presumably major caravan networks and those that were more peripheral to principal caravan routes. Sourcing from contemporary household-level assemblages may serve to differentiate such pooling (Figure 2-4), as was attempted with Oaxaca obsidian by Pires-Ferreira (1976). In the south-central Andes, stronger evidence for differentiating caravan trade from down-the-line trade may come from differences in artifact form and context from a variety of non-local products. In short, differentiating caravans from down-the-line exchange will require inference from multiple lines of evidence and from domestic contexts, evidence that is extremely scarce in the south-central Andes.