Chipping Away
by Alex Hawes
For centuries, the use of tools was believed to separate humanity from the animals. However, in the 1960s, Jane Goodall discovered that wild chimps manipulate branches and stems for use in getting honey out of hives and termites out of their mounds. Other discoveries of tool use by animals soon followed. Chimps also carry rocks around, which they use to crack open nuts. Orangs hold large leaves over themselves to protect them from sun or rain, throw sticks at humans in self-defense, and chew up mouthfuls of leaves to make sponges to soak up rainwater. Even sea otters use tools; they have been witnessed using rocks as anvils against which they smash open mollusk shells for meat.
If humans aren't alone in tool use, what else makes humans special? Some have argued that humans are unique because we use tools to make tools (another step in the cognitive ladder). Hominid fossils, dated as far back as two and a half million years, have been found associated with stone "flakes," sharp shards of rock that may have been used to cut apart animal carcasses. Flakes are formed by smashing one rock onto another. Making sharp flakes is not as easy as it might seem. In addition to generating enough force, the angle of the blow and its position on the rock are crucial.
Stone-tool expert Nick Toth, an anthropologist renowned for carrying rocks with him in his briefcase wherever he goes, wanted to know whether apes could create the same types of tools early human ancestors fashioned from stone. Toth and Sue Savage-Rumbaugh, who has studied the bonobo Kanzi's use of sign language, created a "tool station," consisting of various rocks and a box containing food, secured with a thick rope. In front of Kanzi, Toth banged rocks together, in a very precise manner, to form rock flakes sharp enough to cut rope. Toth then used the best flakes to cut the rope to get a treat for himself. Without any active tutoring, Kanzi learned the importance of selecting the sharpest rocks, and then on his own began trying to make sharp flakes, imitating Toth's methods.
At one point, a frustrated Kanzi handed the stones to Savage-Rumbaugh, in an appeal for her to make the flakes for him. Refused this request, Kanzi seemed to reflect for a few moments, and then stood up and threw the stone against the hard floor, shattering it into shards. He had overcome the problem with a novel solution. The scientists then thought to put in a soft carpet to prevent this from happening again. Once again, Kanzi outwitted them. He pulled up a corner of the carpeting, revealing the hard floor, and smashed the rock against it.
On one other occasion, while working with the tools outside, Kanzi came up with yet another novel approach: throwing the rock against a large boulder to break it apart. Thus, Kanzi came up with new solutions three times in his quest to form the proper tool for the task. In addition to his invented techniques, Kanzi has been able to form flakes in the conventional manner employed by Toth. Yet, given the choice, Kanzi will select and use one of Toth's creations over one of his own. The bonobo has been observed running his fingers along the edges of Toth's flakes, apparently impressed by his workmanship. Toth's flakes simply are bigger and sharper--and therefore more useful--than the ape's. Despite being much stronger than an average human, Kanzi appears unwilling to use all of his force. Perhaps he's afraid of striking the hand he uses to hold the stone in place. Lacking the manual dexterity of humans, Kanzi also may not be able to grip stones as tightly as we can.
Nonetheless, Savage-Rumbaugh emphasizes that it is the process, not the actual end product, that is the most important component of the bonobo's use of stone tools. Kanzi has demonstrated a clear understanding of the concept of using one tool (a rock) to form another tool (a flake). Another piece of the perceived pillar of human uniqueness seems to have been chipped away.
(ZooGoer 24(6) 1995. Copyright 1995 Alex Hawes. All rights reserved.)
First Words (evolution of human speech)
Chipping Away (tool use)
Mindful of Thought (National Zoo's Think Tank)
