Tool Use

Tool Use

Until quite recently, tool use was considered to be a uniquely human behavior. Early anthropologists taught that the use of tools was limited to Homo sapiens and used the presence of tools as an indicator of the presence of humans. Even after tool use by earlier Homo species was demonstrated, anthropologists still insisted that tool use made the species human.

More recently, scientists have observed many different animals using tools. Sea otters use rocks as anvils to break open shellfish. Galapagos finches mold twigs to probe holes in trees to obtain insect larvae. Egyptian vultures use rocks to crack open ostrich eggs. The burrowing wasp, Ammophila, uses a small pebble to hammer down the soil over its nest of eggs. And green herons use bait to attract small fish.

Since nonhuman animals were clearly observed to be using tools, anthropologists reconsidered their earlier position and decided that the making of tools was the uniquely human characteristic. However, in 1960 Jane Goodall and others observed chimpanzees in the wild breaking off twigs from trees, stripping away the leaves, and using the twigs to extract termites from their nests. Since the twig had to be modified by removing its leaves, this activity clearly demonstrated toolmaking. Captive Asian elephants have often been observed to use branches to swat flies. The branches are modified by shortening and removing side branches. Recently, wild Asian elephants have been seen demonstrating the same tool-using and toolmaking behavior.

The environment must possess two characteristics in order for tool use to evolve among a population of animals. First, there must be some evolutionary advantage in tool use. For example, the animal must be more successful at finding food, avoiding predators, or reproducing. Second, objects in the environment that will make useful tools must be available. Chimpanzees use twigs, wasps use small stones, and finches use cactus spines. Without access to these objects, the tool-using behavior would never evolve. The following examples illustrate how Egyptian vultures, woodpecker finches, green herons, and chimpanzees gained an evolutionary advantage from tool use.

Egyptian Vultures

An Egyptian vulture, Neophron percnopterus, has been observed breaking open ostrich eggs, too hard to open by pecking, by throwing a stone held in its beak at the egg shell. The bird's aim is quite good. According to reports by Jane Goodall, the vultures will wander as far as 50 meters (165 feet) from the egg to find a suitable rock.

The rock most often chosen is an egg shaped. This suggests that the vultures have modified an earlier behavior. Many birds throw or drop eggs to break them. John Alcock has suggested that the vultures originally threw or dropped eggs to break them open. The use of rocks to break the eggs open probably began when a vulture accidentally hit an egg with a rock. They then evolved from throwing the eggs to throwing rocks at the eggs. The movement the vulture makes when breaking an egg with a stone is almost the same as the movement the vulture makes when pecking at an egg to break it.

Observations by Chris Thouless and his co-workers of young, handreared vultures demonstrated that the stone-throwing behavior is innate or instinctive, not learned. Young vultures exhibit the behavior once it is linked to a food reward. In the wild, encountering a broken ostrich egg probably rewards young vultures. Thouless also observed that all vultures preferred to throw rounded-off, egg-like stones.

Woodpecker Finches

Charles Darwin observed many species of finches inhabiting the Galapagos Islands and theorized that all of them evolved from a single-species population that had somehow made it to the island. The woodpecker finch, Geospiza pallida, that resides there is one of Darwin's finches. It is called the woodpecker finch because it has evolved the ability to pry insect larvae out of holes in a tree by using a cactus spine or other long, thin tool.

A woodpecker's long, barbed tongue enables it to extract grubs from branches without the assistance of a tool. The woodpecker finch has a short tongue, however, so it has developed the ability to grasp a cactus spine in its beak and pry grubs out of the hole. After extricating the grub, the finch holds the spine under its foot while eating the grub. The cactus spine is carried from branch to branch and used again and again.

Researchers have discovered that woodpecker finches are more likely to adopt tool-using behaviors as hunger increases. In an experiment a different finch, the cactus ground finch, was placed in a cage near a group of tool-using woodpecker finches. The large cactus ground finch does not normally use tools to probe for grubs in its natural environment but it apparently acquired the habit after observing the woodpecker finches at work. Other species of finches did not learn to use tools after observing woodpecker finches.

One researcher happened to observe a young woodpecker finch apparently perfecting the skill of using the cactus spine by observing another finch. This young finch first tried to get grubs from a tree branch using its beak. Since this did not work, the young finch tried using a twig. Then it apparently observed another finch modifying a twig for use and copied the behavior. Scientists have also observed woodpecker finches modifying long cactus spines to form more manageable tools. This is a clear example of toolmaking.

Green Heron

A few green herons have been observed dropping small objects onto the surface of the water. When small fish swim to the surface to investigate the object, the heron grabs the fish. This is apparently not innate behavior because only a few individual birds practice it. Attempts to teach herons to use bait have also been unsuccessful, so why a few do it is not clear.

It may be behavior learned through experience. Perhaps a bird accidentally drops a small object in the water and sees that small fish are attracted. If the heron is able to make the connection between dropping the bait and catching a fish, this indicates a level of cognitive ability beyond what is considered normal for these birds. Perhaps only exceptionally intelligent birds are able to learn the behavior.

Chimpanzees

Chimpanzees have given us the first and clearest example of tool use and toolmaking in a nonhuman species. In Tanzania, chimps regularly construct tools from grass and twigs that they use to extract termites from termite holes. The chimp carefully selects an appropriate stem or twig, modifies it as necessary, and then uses its strong fingernail to dig a hole in the termite mound. As termites rush to repair the damage, the chimp carefully inserts the twig into the hole and just as carefully withdraws the twig. Invariably, several termites are clinging to the twig, which the chimp eats.

These insects are a good source of protein and fat, so they are a valuable addition to the chimp's diet. Wild chimpanzees have also been seen using sticks to get honey from beehives and dig up edible roots. They also use sticks to pry up the lids of boxes of bananas left by scientists.

Twig using is at least partially learned behavior . After extensive observations, Jane Goodall concluded that young chimps learn how to break twigs from trees, strip away the leaves, and insert them into termite holes by imitating adults. This is a complex and involved behavior. Without the adults to demonstrate, young chimps would probably never become skillful. However, the behavior is also at least partly innate. All young chimps play with sticks and twigs and entertain themselves by poking the sticks into holes.

If neither tool use nor toolmaking distinguish humans from other animals, is there any aspect of tool use that is still uniquely human? The answer is, possibly, no. It is conceivable that intelligence and tool use lie along a spectrum and humans just have more of the characteristic. The difference may be quantitative instead of qualitative. But, it is also possible that the regular, extensive use of tools to solve everyday problems is a distinctly human characteristic. The regular and consistent use of tools frees humans from limits imposed by our anatomy. It is even possible that regular tool use has somehow encouraged the development of problem-solving skills.

see also Learning.

Elliot Richmond

Bibliography

Alcock, John. Animal Behavior: An Evolutionary Approach, 6th ed. Sunderland, MA: Sinauer Associates, 1998.

Beck, Benjamin B. Animal Tool Behavior: The Use and Manufacture of Tools by Animals. New York: Garland, 1980.

Ciochon, Russell L., and John. G. Fleagle. Primate Evolution and Human Origins. Menlo Park, CA: Benjamin/Cummings, 1985.

Curtis, Helena, and N. Sue Barnes. Biology, 5th ed. New York: Worth Publishing, 1989.

Greenhood William, and Robert L. Norton. "Novel Feeding Technique of the Woodpecker Finch." Journal of Field Ornithology 70 (1999).

Goodall, Jane. (1986). The Chimpanzees of Gombe: Patterns of Behavior. Cambridge, MA: Belknap Press, 1986.

Goodall, Jane, and Hugo van Lawick. "Use of Tools by Egyptian Vultures, Neophron percnopterus. " Nature (1966):468.

Lack, David. "Darwin's Finches." Scientific American (April 1953):68.

Roberts, William A. Principles of Animal Cognition. New York: McGraw-Hill, 1997.

Schultz, Adolph H. The Life of Primates. New York: Universe Books, 1972.

Thouless, C R., J. H. Fanshawe, and B. C. R. Bertram. "Egyptian Vultures Neophronpercnopterus and Ostrich Struthio-camelus Eggs: The Origins Of Stone-Throwing Behavior." Ibis 131 (1989).