ANIMAL TOOLS

"Tools maketh man," so said Kenneth Oakley, the pre-historian. He meant that only human beings make tools of flaked stone. More generally, many species of animals make and use tools, both in nature and in natural captivity, from wasps to finches to apes, but many more do not. Few species have tool kits (repertoires of different types of tool for different purposes) or tool sets (two or more kinds of tools used in series to perform a task). Making sense of such behavioral variation is a challenge to scientists.

Tools

Definitions of tools vary (Beck 1980). In this entry, the following is used: a detached inanimate object used by a living creature to achieve a goal, typically to alter the state or position of another object. This includes constructing a nest, but not reclining on a bough, and cracking a snail with a stone but not with the teeth. It excludes glaciers moving stones across landscapes, but includes sea otters retrieving stones from the seabed. If these actions entail modifying the object so that is it more effective, then tool using becomes toolmaking. Tools can also be classed by function: subsistence (digging stick), social life (weapon), or self maintenance (napkin), or by mode of action: percussion (nut cracking), probe (termite fishing), barrier (leaf umbrella), and more.

For as long as scientists have paid attention to animal tool use, two vertebrate classes, birds and mammals, have predominated. Some examples are classic. California sea otters crack open mollusks on anvil stones balanced on their chests as they float on their backs (but their Alaskan cousins do not). Beavers fell trees and shrubs to construct dams and lodges that transform landscapes and watersheds. Woodpecker finches of the Galapagos Islands detach twigs or spines and use them to probe and to extract insects from cavities in woody vegetation. More magnificently, bowerbirds in Australia and New Guinea build and decorate complex structures and arenas. These edifices, which range from walls to spires, are not nests for residence or rearing young, but instead serve as advertisements by males to court females.

All of these examples of tool use vary across populations within a species or across individuals within populations. In many cases, they are one-trick ponies, that is, single, specialized adaptations: Sea otters in Monterey Bay that use anvil stones do not engage in any other type of tool use. The prize toolmaker among birds is probably the Caledonian crow of the south Pacific island of New Caledonia, which uses three types of tool in extractions foraging. By comparing twenty-one populations, scientists determined that tools have diversified over time and across space.

Some creatures with large brains (and so presumed high intelligence) even manage tool use without grasping appendages. The bottle-nosed dolphins of Shark Bay in western Australia carry sponges on their noses. Apparently they use these to root out prey from the sea floor, with the sponge serving as a glove to protect the rostra from abrasion.

Of the orders of mammals, the primates are the main tool users, especially the great apes (McGrew 1992). Apart from them, it is the capuchin monkeys of Central and South America that are best known for their tool behavior. Their use of wood or stone anvils to smash open hard-shelled fruits is widespread in rainforests. In harsher habitats, capuchin monkeys are even more enterprising: In the dry open country scrublands of Brazil, they use stones as hammers to crack nuts on anvils, and even as trowels to dig up tubers.

Of the four species of great apes (bonobo, chimpanzee, gorilla, and orangutan), there is surprising variety in nature despite the fact that in captivity, all show similar levels of intelligence. Wild gorillas, whether in lowland forest or on alpine slopes, exhibit no tool use. Similarly bonobos show little, apart from occasional use of leaves as rain shelters or felled saplings in branch-dragging displays; notably absent in these apes from the Democratic Republic of Congo is any tool use in foraging. Orangutans, in some high-density wild populations in Sumatra, are accomplished arboreal tool users, but their special feature is oral tool use, presumably because their hands are needed for support in the forest canopy. Using skillful movements of lips and teeth, tools of vegetation are used to process fruits with stinging hairs and to extract insects from rotten wood.

The champion tool user and maker of the animal kingdom is the chimpanzee, seen in captivity for more than eighty years from the experiments of Wolfgang Köhler and for more than forty years from the field observations of Jane Goodall. More than fifty populations of these wild apes across eastern, central, and western Africa are known to use tools (McGrew 2004). These include flexible probes made of vegetation to fish out termites from underground nests or ants from the cavities in trees, hammers of stone or wood to crack open nuts on anvils of root or stone, pestles of palm frond to smash the mortared heart of palm, crumpled leaves to sponge out water from tree holes, and leaves to wipe off bodily fluids in personal hygiene. Tools are transported from worksite to worksite, and sometimes are made in advance of use or kept to be used again. Termite fishing has been followed through four generations of chimpanzees at Gombe National Park in Tanzania. There are limits, however: No wild chimpanzee has yet been shown to purposefully modify stone for use as a tool, nor to use one tool to make another.

Technology

When the use of tools increases efficiency or convenience, or reduces risk, or opens up new ways to exploit resources, old or new, this knowledge is termed technology. As such, when time or energy is saved, or tasks are made easier or more comfortable, or danger to life or limb is lessened, or innovations yield new payoffs, however elementary, these may be thought of as the basis of material culture. When such techniques are invented and passed on by socially mediated processes of transmission, they come to approximate what in humans is called culture. Transmission within a generation is called horizontal; transmission passed down from one generation to the next is called vertical. The latter is termed tradition. This requires some form of social exposure or interaction between knowledgeable and naïve individuals, which may range from passive observational learning to active teaching. It takes careful experimentation to establish which mechanisms of transmission of knowledge are present, but in the end, what matters most is what technological transfer occurs, not how it gets done.

All known examples of technology in animals, as defined here, come from great apes. Often the first clue comes from observed behavioral diversity in wild populations (Whiten et al. 1999). The chimpanzees of Mahale ignore the fruits of the oil palm; those at Gombe eat the outer husk only and without tools; those at Tai crack open the nuts to extract the kernel; and those at Bossou sometimes modify the orientation of the anvil to make their nut cracking more efficient. The predator (ape) and prey (nut) are the same in all four places; what differs is technical knowledge. Similar cross-cultural differences have been reported for orangutans in Borneo and Sumatra (van Shaik et al. 2003), and bonobos in the Democratic Republic of the Congo (Hohmann and Fruth 2003). Recently studies of technology in animals have extended into the past, with archaeological excavations of chimpanzee nut cracking sites in Ivory Coast. These have yielded fragments of stone, and so give enduring time-depth to nonhuman technology (Mercader et al. 2002).

Are the differences between the elementary technology of nonhuman species and the more complex technology of human ones of degree or kind? This depends on the feature chosen for comparison: Some textbooks state that a key difference is that only humans depend on technology, while for other animals it is somehow optional. The logic is that because all human societies show technology, there must be dependence, but all known wild chimpanzee populations studied in the long term also show technology, so by the same yardstick they too depend on it. On other grounds, there seem to be differences: No known animal technology seems to be imbued with religious or supernatural significance, though it is hard to infer meaning from behavior.

These findings have not only scientific implications for the understanding of humans but ethical implications for the treatment of animals. Animals kept in captivity, but deprived of appropriate objects to manipulate (explore, play, and construct), may lead incomplete or distorted lives. Impoverished of raw materials, they may fail to show species-typical behavior, such as shelter making, or worse, develop abnormal patterns, such as coprophagy. Ecologically valid environmental enrichment means using the findings of field research to provide species-specific contexts for tool use and social settings for technology if animals are confined. This can be done through emulation (seeking to recreate nature, e.g., bamboo plantings) or simulation (seeking to mimic key features of nature, e.g., artificial termite mounds).

WILLIAM C. MCGREW

SEE ALSO Evolutionary Ethics;Ethology;Sociobiology.

BIBLIOGRAPHY

Beck, Benjamin B. (1980). Animal Tool Behavior. New York: Garland STPM Press. Twenty-five years after publication, this remains the "bible" on animal technology, as a comprehensive review of the literature and theoretical treatise on tool use from insects to apes.

Hohmann, Gottfried, and Barbara Fruth. (2003). "Culture in Bonobos?: Between-Species and Within-Species Variation in Behavior." Current Anthropology 44: 563–571.

McGrew, William C. (1992). Chimpanzee Material Culture: Implications for Human Evolution. Cambridge, UK: Cambridge University Press. Chimpanzee tool use reviewed and explained in terms of cultural processes as these might shed light on the evolutionary origins of human technology.

McGrew, William C. (2004). The Cultured Chimpanzee: Reflections on Cultural Primatology. Updates Chimpanzee Material Culture (1992) and expands discussion into related aspects of non-material culture; written in opinionated and accessible style. Cambridge, UK: Cambridge University Press.

Mercader, Julio; Panger, Melissa; and Christophe Boesch. (2002). "Excavation of a Chimpanzee Stone Tool Site in the African Rainforest." Science 296: 1452–1455. First attempt to practice archaeology on apes, by excavating stone artifacts from West African chimpanzees' nut-cracking sites.

van Schaik, Carel P.; Ancrenaz, Marc; Borgen, Gwendolyn; et al. (2003). "Orangutan Cultures and the Evolution of Material Culture." Science 299: 102–105. Following Whiten et al. (1999), researchers on wild orangutans find behavioral variation across populations of these apes in Borneo and Sumatra.

Whiten, Andrew; Goodall, Jane; McGrew, William C., et al. (1999). "Cultures in Chimpanzees." Nature 399: 682–685. Trail-blazing synthesis comparing behavioral diversity in seven populations of wild chimpanzees across Africa.