tool use

Most people know that hunter-gatherer men hunt meat. Fewer people know the major secondary target for male foraging in many hunter-gatherer societies: honey. The resource is so highly valued that some men spend as much effort foraging for honey as they do hunting.

Chimpanzees also forage for honey. The use of tools to dig for, bash into, and dip honey out of bee nests or hives has long been known from many chimpanzee field sites. For example, Craig Stanford and colleagues (2000) described how chimpanzees in Bwindi-Impenetrable National Park, Uganda, use small sticks to forage for honey from the small nests of stingless bees, while they use much bigger sticks to get honey out of honeybee nests.

Two papers from this year have illustrated a new appreciation for the complexity of chimpanzee toolkits used for honey raiding. Crickette Sanz and David Morgan (2009) describe honey gathering by chimpanzees at the Goualougo, Congo field site, while Christophe Boesch and colleagues (2009) describe the technology used by chimpanzees at Loango, Gabon. Both are relatively new field sites, in which researchers have arrived recently or are still habituating the chimpanzees to their presence. Thus, the variations in chimpanzee behaviors at these sites are still being recognized and just starting to be reported.

Loango National Park is a relatively new field site. As the researchers there continue to habituate the chimpanzees, they have been gathering a series of observations on behaviors that occur differently in Loango compared to other field sites. According to Boesch et al. (2009:2), chimpanzees at the Loango field site do not crack nuts despite a local abundance of them. But far from being simpler in their material culture than other chimpanzees that do crack nuts, the Loango chimps make up for their lack of nutcracking with a complex package of tools for honey extraction:

Gathering honey from underground hives, similar to underground termite fishing in Goualougo, is special in the sense that chimpanzees cannot see where the resource is hidden and use the first tool, the perforator, as an exploratory tool to “feel” where the resource is located underground. In both cases, external indirect signs of food sources are visible (e.g., large termite mounds or small fragile Melipone-made tubes), but the nest itself is not visible and its exact location cannot be inferred. Therefore, chimpanzees have to investigate the soil in order to locate food that can be, in the case of Melipone underground nests, as much as 1 m deep and 70 cm lateral to the visible tube. Locating the underground chamber can take a human between 20 to 40 minutes (Boesch, pers. obs.). The successful locating of honey is apparent from honey sticking to the ends of perforators. To extract honey, a tunnel needs to be dug sideways so as to reach the underground chamber and prevent soil from getting mixed with the honey once the membrane of the chamber is broken (in general, the intact upper membrane of the chamber in the emptied hole can be felt). We think that such tunnels are dug with the help of perforators to loosen the soil. These tunnels are sometimes barely large enough to let a human arm through, and therefore indicate that chimpanzees know exactly where they are aiming. This cannot be done by simply following the bee tube, as it is much too fragile to resist the tool-assisted digging process. Thus, an elaborate understanding of unseen nest structure, combined with a clear appreciation that tools permit the location of unseen resources, and a precise three-dimensional sense of geometry for reaching the honey chamber from the correct angle, is demonstrated by the chimpanzees when extracting underground honey. It has been proposed that an elaborate understanding of causal relationships between external objects is required for flexible tool use to evolve (Boesch and Boesch-Achermann, 2000), and the fact that such exploratory tools are only seen in chimpanzees and humans supports this proposition (Boesch et al. 2009).

I liked the authors' description of how they defined tool types and categorized objects on the basis of signs of use. WIth quite a simple technology, this differentiation appears nevertheless to be of a similar extent to the stone toolkits used by early Homo. What is different is the complexity of manufacture of (some of) the elements of the toolkit.

That topic of basic manufacturing method versus within-toolkit differentiation is addressed by a new study by Thibaud Gruber and colleagues (2009):

Here, we present the results of a field experiment [20] and [21] that compared the performance of chimpanzees (P. t. schweinfurthii) from two Ugandan communities, Kanyawara and Sonso, on an identical task in the physical domain—extracting honey from holes drilled into horizontal logs. Kanyawara chimpanzees, who occasionally use sticks to acquire honey [4], spontaneously manufactured sticks to extract the experimentally provided honey. In contrast, Sonso chimpanzees, who possess a considerable leaf technology but no food-related stick use [4] and [22], relied on their fingers, but some also produced leaf sponges to access the honey. Our results indicate that, when genetic and environmental factors are controlled, wild chimpanzees rely on their cultural knowledge to solve a novel task.

The finer points of tool use lie atop a technological substrate. For one group of chimpanzees, this substrate may be sticks, for another stones (in nutcracking), for another leaves. Social learning may tend to associate some raw materials with manipulatory processes -- a chaïne operatoire, at a very simple level. The complexity of the honey-extraction kits appears to show that, at least for highly valued purposes, chimpanzees can bring together distinct elements into a single technological solution. It's nothing that a three-year-old human can't do, but it's another point in favor of Wynn and McGrew's "Ape's view of the Oldowan" argument.

References:

Boesch C, Head J, Robbins MM. 2009. Complex tool sets for honey extraction among chimpanzees in Loango National Park, Gabon. J Hum Evol 56:560-569. doi:10.1016/j.jhevol.2009.04.001

Gruber T, Muller MN, Strimling P, Wrangham R, Zuberbühler K. 2009. Wild chimpanzees rely on cultural knowledge to solve an experimental honey acquisition task. Curr Biol (in press) doi:10.1016/j.cub.2009.08.060

Sanz CM, Morgan DB. 2009. Flexible and persistent tool-using strategies in honey-gathering by wild chimpanzees. Int J Primatol 30:411-427. doi:10.1007/s10764-009-9350-5

Stanford CB, Gambaneza C, Nkurunungi JB, Goldsmith ML. 2000. Chimpanzees in Bwindi-Impenetrable National Park, Uganda, Use different tools to obtain different types of honey. Primates 41:337-341.

Christopher Bird and Nathan Emery (2009) performed a number of tool use experiments on rooks -- birds related to crows (corvids) that do not use tools in the wild. Some other corvids, in particular New Caledonian crows, are expert tool users. People who work with New Caledonian crows compare their tool prowess with the great apes -- they can manufacture novel implements, put together two items into a compound tool, and use tools to make other tools. Each of these is a test that psychologists devised to differentiate human tool manufacture from animals. In each case, apes passed, and then the New Caledonian crows passed.

In the current paper, Bird and Emery find that rooks also can do these things, despite never having been observed to do any of them in the wild. They conclude that the birds likely do not have specialized cognitive adaptations for tool manufacture, but instead that they are solving novel problems using cognitive skills that are also useful for many other kinds of problems -- in short, domain general cognition:

Our results contradict suggestions that tool use was the driving force behind the evolution of advanced physical intelligence (2). It appears more likely that corvid tool use is a useful by-product of a domain-general “cognitive tool-kit” (31) rather than a domain-specific ability that evolved to solve tool related problems. Whether or not each species taps into this capacity for tool use may depend on their ecology (22, 32).

In hominoids, a shared basic ability for tool manufacture goes back at least to the Middle Miocene, based on its phylogenetic distribution. It is an open question whether early apes also were tool users. Some monkeys make and use tools in the wild, and if their abilities are homologous with ours, that would put the cognitive capacity for tool manufacture back into the Oligocene. Bird and Emery go through a similar train of logic for the corvids:

Rooks are highly innovative, social foragers (39), using their cognitive abilities in a number of nontool related ways (40). Our findings provide further support for recent claims of convergent evolution in the cognitive abilities of corvids and apes (31). New Caledonian crows and now rooks have been shown to rival, and in some cases outperform, chimpanzees in physical tasks, leading us to question our understanding of the evolution of intelligence.

The claim is that the cognitive resources useful for tool manufacture are probably also useful for other things, and therefore conserved in many if not all corvids. If they're useful for other things, there's no necessary reason for them to have evolved as adaptations for tool use or manufacture (although tool use in ancestral corvids remains possible). The same may be true of primates. For example, gorillas process some kinds of plant foods in complicated ways, using series of steps comparable in complexity to chimpanzee tool manufacture. But gorillas use tools very sporadically in the wild. Arguably, general-purpose cognitive abilities underlie both kinds of activities -- and social learning would facilitate both kinds of skills.

References:

Bird CD, Emery NJ. 2009. Insightful problem solving and creative tool modification by captive nontool-using rooks. Proc Nat Acad Sci USA 106:10370-10375. doi:10.1073/pnas.0901008106