4. Exaptive Tool Use: Equipotentiality

Similar and related to retooling is Equipotentiality. This new concept was first coined by John McNab (pers. comm. 1996), but defined and developed further by Preston (1999). It is defined as tools (both formal and non-formal) that were originally manufactured for one task and then reused for another. It is largely inspired and based on the biological concept of exaption (also known as exaptation), although no evolutionary connotations are implied here. Exaption is concerned with the process and product of evolution where a structure, organ or behavioural trait that was previously shaped by natural selection for a particular function (an adaptation), is co-opted for a new use (Gould and Vrba 1982), e.g. bird feathers initially evolved for temperature regulation but later evolved for flight. Thus for chipped stone tools equipotentiality (or exaptive tool use) implies that tools can be either modified before reuse, and hence used as blanks, or used without modification and use-wear modifies them (e.g. the battering on a core or axe used as a hammer stone). It also implies that even if a tool was manufactured (designed) for specific tasks it can be used (theoretically) in many different ways: hence equal potential or the alternative soubriquet of flexible tool use.

As a concept, equipotentiality depends firstly on the idea of intended formal tool design: originally constructed with a particular purpose in mind (not to be confused with the piece as we find it and being the last in a series of operational chains). Secondly, it depends on reuse/recycling of a tool, which covers both the opportunistic and versatile tool design categories and represents an economising strategy-cost (effort) efficiency associated, for instance, with distance from a raw material source.

Although both retooling and equipotential tool use may produce the same signature (i.e. modified tools), the main difference is in the intention behind the processes. Equipotentiality is recycling/using a tool as a blank to make a new implement (i.e. redesign it for a different task than that originally intended), whereas retooling is simply resharpening to allow the continued use of that tool for the same purpose. Thus the difference is a question of context. For instance, for tranchet axes we would expect to have resharpening (retooling) with the removal of the tranchet flake. Equipotentiality, on the other hand, is most easily seen where resharpening is not expected, such as the burination on a scraper (in this case using the scraper as a blank). For an axe to be used exaptively it could be used as a hammer stone or as a core.

Traditionally, chaîne opératoire has described knapping and tool production in terms of primary (debitage/blank production) and secondary knapping (retouch) (e.g. see Odell 2003). This clearly does not accommodate retooling and equipotentiality. Thus, I propose that equipotentiality and retooling necessarily must imply tertiary modification. Therefore taking into account the defined differences between retooling and equipotentiality, we can describe the former as passive tertiary modification, where the tool morphology is being changed but only through continued use, not to change its design intentionally, and the latter as proactive tertiary modification. Equipotentiality is described here as proactive because the tool and morphology of the piece are purposely and actively transformed into a new design. Both these ideas clearly accommodate what Finlay (2000) called multiple authorship, but in this case on different operational and temporal forms and stages.

It is therefore my view that the relationship between tertiary modification and tool morphology is important because 1) tertiary modification must necessarily imply a change in tool shape; and 2) when a tool is regularly discarded at the same place it necessarily represents a potential resource.

Another significant implication is if the lithic we find is the last in a series of operational chains then there are inferences for the use of microliths as social indicators. Typological studies have assumed that the form we find was the intended shape (see critiques in Finlay 2000; Preston 1999). However, chaîne opératoire, retooling and equipotentiality show that this is not necessarily the case. So while particular combinations of microliths may be seen as individual solutions to projectile construction (Jacobi 1978), we should be cautious of the assertion that they are indicative of a social group, since it has been demonstrated that microlith shape could easily be changed by retouch/retooling undetectable to the analyst (Barton and Neeley 1996; Finlay 2000). This is also reminiscent of Finlayson et al. (1996, fig. 16.1), who demonstrated that microliths tend to grade from one shape to another (see Fig. 3). Also, as part of composite tools microliths were covered in mastic so their actual morphology, which is claimed to be a cultural emblem, was concealed and hence could be of no practical stylistic or totemic cultural value (Finlay 2000), other than perhaps as the result of traditional (habitual) ways or norms of manufacture taught by a knapper to an apprentice.

Figure 3: An example of microlith morphological variability (after Finlayson et al. 1996)

There are two reasons that Mesolithic groups would have employed equipotential tool use. One, as a lazy alternative to obtaining fresh raw material and manufacturing a new tool. That is, the nearest piece of usable flint (in this case a discarded tool at a site) was picked up and modified for the task in hand. This behaviour was replicated in a contemporary experiment I undertook, in which 100 subjects were asked to prepare and butter toast and were provided with knives, forks and spoons and various other tools. Where knives were freely available they used them to spread butter. However, if all the knives were deliberately left dirty around 50% of the subjects would habitually use a spoon to spread butter (rather than wash a knife). That is, use a tool designed for another purpose for the task in hand – equipotentiality. Though trivial, the experiment seemed to suggest this was a consistent and repeatable behaviour that took the path of least resistance, although more experiments need to be undertaken to substantiate this further.

Another more significant reason was as an expedient or economising strategy, possibly as a response to pressure on resources from either increased distance from raw material source (and hence effort) or scarcity of good-quality material that forces discarded materials to be reused for expedient tasks. This sort of behaviour has been described as a cost-effective way of obtaining materials when the available resources are exhausted or scarce (Bamforth 1986; Camilli and Ebert 1992; Barton et al. 1995).

Equipotential tool use, in my opinion, was an essential part of the Mesolithic technological ethos; this is also implied by the fact that microliths were flexible and multi-functional in that they could be used in many different composite tools (Butler 2005; Clarke 1978). This flexible tool-using behaviour is consistent with the approach that equipotential tool use presents, for instance, flexibility in approach, categories, and what blanks/tools can and were used for.

One particularly prominent example of equipotentiality in Clark's (1954) assemblage are the scraper-burins, where end scrapers were later used as a blank, burinated and used as a burin. Such combination tools have been recorded from throughout the Upper Palaeolithic, Mesolithic and later prehistory (Butler 2005). My technological attributes analyses of the formal tools from Clark's (1954) Star Carr assemblage and my ongoing research of Central Pennine Mesolithic sites seems to suggest some equipotential behaviour during the Mesolithic (see Fig. 4 – opens PDF).

Other evidence of equipotentiality at Star Carr consists of the bones that were retouched (see Clark 1954, fig. 73).

Moreover, microwear studies (Dumont 1985; 1988; 1989) have demonstrated that many of the tools from Star Carr were often used for more than one task. For example, a scraper was used with different actions to work on the same material: scraping in one task and planing in another. In another example, Dumont demonstrated that burins were used for incising, drilling, scraping and planing. He also found that less than 1% of the microliths at Star Carr had use-wear. Thus were these unused microliths a cache? Dumont compared the findings to a morphological study and inferred that the tools at Star Carr were manufactured to a set mental template. This is interesting, as according to my study many of these (see Fig. 4) were then reused exaptively.

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