Tool use and construction

Tools can be defined as detached objects that are used to achieve a goal. Achievement of the goal can involve manipulation of some aspect of the environment, including another organism. The making of tools involves modifying some object in the environment for use as a tool, but not all objects used as tools by animals are constructed.

Instances of tool use and tool construction have been observed in great apes and monkeys living in captivity. All species of great ape have been observed to make and use tools in captivity. Some monkeys have been observed to use tools and occasionally to construct tools in captivity. Observations of tool use and construction by nonhuman primates in the wild have been less widespread. This difference between demonstrations of tool use in captivity and the natural environment may exist because, for the most part, evolutionary adaptations of the animal may sufficiently address challenges in the natural environment. However, environmental contingencies in captivity may be unique in encouraging tool use. In studies of tool use, researchers set up problems that are best solved using tools. In captive environments, experience with such problems coupled with extensive experience with tool-like objects provide the environmental and cognitive scaffolding that facilitate the demonstration of tool use by animals who may not so readily demonstrate such capacities in their natural environment.

However, instances of tool use and construction have been observed in great apes in the wild, particularly in the chimpanzee. The most widely known of these is the chimpanzee's use of twigs to "fish" for termites in termite mounds at the Gombe Stream Reserve (now Gombe National Park) in Tanzania, East Africa. Following the report of that first observation by Jane Goodall in 1968, many instances of tool use and tool construction have been discovered in chimpanzees and other animals in their natural environment. For termite fishing, the choice of an appropriate branch, twig, or grass blade involves judgments of length, diameter, strength, and flexibility of the tool. Any leaves remaining on a branch are removed, and the tool is dipped into holes in the termite mound. Termites attack the intruding stick, attaching themselves to it, and the chimpanzee withdraws a termite-laden stick and proceeds to eat the termites.

Additional observations of tool use include the use of leaves that have been chewed to serve as a sponge to obtain water from tree hollows, the use of tree branches in agonistic displays, various uses of sticks, leaves, or branches to obtain otherwise inaccessible food, and the use of leaves to remove foreign substances from the body. Orangutans in the wild have been observed to use leaves as sponges and as containers for foods. They use tools to aid in opening large strong-husked fruits and to protect them from spines on the outside of fruits.

An interesting complicated instance of tool use is the use of rocks as hammer and anvil to crack open nuts reported for chimpanzees in West Africa. Coula nuts or palm-oil nuts with hard shells are placed on a hard surface and cracked open by hitting them with a hand-held rock. The supporting surface (or anvil) can be a tree root or a rock obtained from the for est floor by the chimpanzee. Rocks used as hammers have a size and shape that fit the chimpanzee's hand, and rocks chosen as anvils have a flat surface. The nut is placed on the flat surface of the anvil and pounded with the hand-held hammer rock. If an anvil has an uneven base that causes it to wobble when the nut is struck, the chimpanzee finds a smaller rock to use as a wedge under the smaller end of the anvil to balance it.

Infant chimpanzees learn tool use as they observe their mothers make and use tools. Observations of mother chimpanzees engaged in explicit teaching of tool use to their infants have been reported at only one site, and on only two occasions. On one occasion, a mother took a hammer rock from her daughter who was holding it in an orientation that was not conducive to nut cracking, and slowly rotated the orientation of the rock to a position that was useful. After the mother finished cracking nuts, her daughter used the rock in the same orientation as her mother had used it. On the second occasion, a mother re-positioned a nut that her son had placed on an anvil in a position that would not have permitted its being opened. The son then used a hammer rock to open the nut. Both of these observations are provocative, but in the absence of other such observations it is not clear that the mother's intent was to teach the infant. Indeed, most learning of tool use and tool construction by young chimpanzees appears to be from observation of the mother's behavior and manipulation of objects used as tools in the context in which they are used.

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