Tools versus nests

Many creatures can use tools of a specific kind, and in some cases, even make them, as do New Caledonian crows (Hunt Reference Hunt1996; Weir et al. Reference Weir, Chappell and Kacelnik2002). Lefebvre et al. (Reference Lefebvre, Nicolakakis and Boire2002) conclude that the complex cognitive processes involved in tool use may have independently co-evolved with large brains in several orders of corvine and passerine birds. Nonetheless, it seems to me that nest building by birds is even more impressive than their tool making is; and indeed, Hansell & Ruxton (Reference Hansell and Ruxton2008) urge that we view tool behaviors as a limited subclass of construction behavior. Nest building in birds has been a key driver of habitat diversification and speciation in these groups (Collias Reference Collias1997; Hansell Reference Hansell2000). It is therefore intriguing that Stewart et al. (Reference Stewart, Piel and McGrew2011) show that re-use of specific nest sites by savanna chimpanzees may be a result of “niche construction” (Iriki & Taoka (Reference Iriki and Taoka2012) Laland et al. Reference Laland, Odling-Smee and Feldman2000) through formation of good building sites within trees. They speculate that environmental modification through construction behavior may have influenced both chimpanzee and early hominin ranging by leaving behind recognizable patterns of artifact deposition across the landscape.

Human tool use in construction

Let us shift attention from “using a tool” to the ability to deploy multiple tools to solve a problem. To join a piece of wood to the wall, I may employ a screw of sufficient length plus a screwdriver or a nail and hammer. I may also employ a stud finder, but if I need to affix an object where there is no stud, I deploy a rawlplug, a drill, and a hammer to prepare for the screw. For household repair, I may deploy these tools and more to solve a truly novel problem by breaking it down into subproblems for which I have routine solutions. Or I may call in a handyman, thanks to the great specialization within human society and the social construction of monetary incentives.

An etymological detour to the Oxford English Dictionary: The word handiwork (“a thing made by the hands”) comes from the Old English hand+geweorc. As geweorc≈iwork did not survive in Middle English, hand-iwerc was reanalyzed as a compound of werc with handi. Handi was eventually treated as an adjective, handy, meaning “of, or done by, the hand” when used in new compounds – including handy-man. The point here is that the refined shape and controllability of the human hand must be complemented by many changes in the brain to yield “handyness.” Of the nine cognitive capacities listed by Vaesen, only three – enhanced hand-eye coordination, body schema plasticity, and function representation – relate directly to using a tool for its intended purpose. Two – causal reasoning and executive control – relate not so much to tool use as to the more general skill of problem solving (of which construction, with or without tool use, is a crucial subcase). The remainder – social learning, teaching, social intelligence, and language – all relate to social interaction in general or the transfer of skills in particular, whether or not they involve tool use.

Vaesen argues that only one of these nine capacities, body schema plasticity, cannot be invoked to explain what makes human technological abilities unique as “we share the trait with our closest relatives.” However, the issue is not whether the body schema can be extended, possibly by extensive shaping as in monkeys (Iriki et al. Reference Iriki, Tanaka and Iwamura1996; Umiltà et al. Reference Umiltà, Escola, Intskirveli, Grammont, Rochat, Caruana and Rizzolatti2008). Rather it is (in part) the uniquely human rapidity and flexibility with which different extensions of the body schema can be deployed in some overall task, switching back and forth between using some part of the body or some part of a tool as the end-effector for the current action (Arbib et al. Reference Arbib, Bonaiuto, Jacobs and Frey2009).

Language

Vaesen distinguishes two routes from tool use to language:

• Advanced tool use promoted manual dexterity that was exapted for communicative purposes; a similar form of fine control was later applied to oral movements, leading to speech.

  Advanced tool use gave humans the capacity to combine and integrate lower-order actions into higher-order units; resources initially devoted to structuring manual hierarchies were exapted for linguistic purposes.

and cites the mirror system hypothesis (Arbib Reference Arbib2005) as an example of the former. However, the actual theory overlaps both and makes no appeal to advanced tool use. Rather, it stresses complex imitation, the ability to recognize and imitate combinations of actions used to reach a perceived goal, together with variations on known actions. Recently, inspired by Stout's (Reference Stout2011) essay on stone toolmaking and the evolution of human culture and cognition, I developed a scenario (still in rather rudimentary form) in which complex imitation underwrites the co-evolution of language and toolmaking, with neither required to reach a critical complexity to initiate the evolution of the other (Arbib Reference Arbib2011; a somewhat modified account appears in Arbib Reference Arbib2012). In this regard, it is useful to think of the grammar of a language not as a very general set of syntactic rules but rather as involving a large number of constructions that provide tools for assembling words hierarchically to meet the communicative goals of both familiar and novel social situations (Arbib & Lee Reference Arbib and Lee2008; Croft Reference Croft2001; Goldberg Reference Goldberg2003; Kemmerer Reference Kemmerer and Arbib2006; Verhagen Reference Verhagen2005).