Chimp Cognition

Chimpanzees and humans are "more closely related to each other than either is to any other living primate" (Begun, 1992). Perhaps you have heard that humans and chimps are "99% identical" in their genetic structure. That is true, but it is a bit misleading. As Plomin and Kuse (1979) point out, the average stretch of human DNA is almost 99% identical to the corresponding stretch of chimp DNA, but small differences in DNA can lead to numerous differences in the proteins generated by the DNA. Comparing proteins from chimps and humans, only about 75% are identical. Still, that is a lot of overlap, so it is not surprising that chimps come the closest to human intelligence of all non-human animal species.

How is the claim that chimps are 99% genetically identical to humans somewhat misleading?


Kohler's chimpanzee Sultan showed "insight" in solving a problem. First he assembled a stick, then piled up boxes, then used the stick to reach a banana dangling from a tree.

What was Kohler's classic study of "insight"?

For a long time, psychologists have been impressed by the intelligence of chimpanzees. Perhaps the most famous example comes from Wolfgang Kohler in his book The Mentality of Apes (1925). Kohler suspended bananas out of the reach of chimpanzees. He found that chimps could assemble two sticks together to make a single instrument to reach the bananas. They also proved capable of piling up boxes to reach the bananas. And they could combine these techniques when necessary.

Kohler claimed the apes were showing insight, coming up with the idea on their own in a flash of intuition. Epstein, one of the behavioral psychologists who showed pigeons how to use mirror images of their bodies, decided to test a behavioral explanation. If Epstein could teach a pigeon to do something similar to Kohler's apes, maybe people would realize there was nothing mystical or mysterious about it

How did Epstein get a pigeon to imitate Sultan's feat?

Epstein could not completely imitate Kohler's observations with pigeons, because a pigeon cannot lift a box. So Epstein had the pigeon retrieve a box from another compartment, climb on it, and peck a small plastic "banana" in order to get grain reinforcement. The experiment worked. First Epstein taught components of the goal behavior. He taught the pigeon to peck at the plastic banana for grain reinforcement. Then he taught the pigeon to push the box around. Finally, as predicted, the pigeon had the "insight" to put these components together when the banana was hoisted out of reach. The pigeon retrieved the box, climbed on it, and pecked the banana.

What were similarities and differences between the two performances?

Kohler's apes were merely combining previously familiar actions. However, creativity always involves combining pre-existing components into new combinations. Kohler claimed that his chimps came up with the solution on his own, based on past experience with sticks, climbing, and bananas. Epstein's pigeon needed long and careful training. So the differences between the two performances may be just as important as the similarities...it depends what point you want to make. Epstein showed that no mysterious, magical abilities were required to explain insight, and that was Epstein's main goal, so he succeeded. Kohler showed that apes were capable of coming up with creative solutions to problems without special training, which was significant in itself.

How did a chimp optimize its hunt for food?

Menzel (1973) studied spatial memory organization in chimpanzees by letting the chimp observe food being hidden in 18 randomly chosen places within a yard. Released from its cage, the chimp quickly gathered the food, following an "optimum" route that minimized the distance traveled. This indicated that it was not merely imitating the route that the humans had taken; it had formed a "mental map" of where the food was hidden and was following its own map.

What did Sands and Wright demonstrate?

Sands and Wright (1980) demonstrated that a rhesus monkey could memorize a list of items. Like humans doing such a task, it showed primacy and recency effects, meaning it showed superior recall of early and late items in the list. The researchers also found that picture memory in monkeys is almost identical to that of humans (Sands & Wright, 1982). Both chimps and humans are exceptionally good at recognizing pictures they have seen the day before.

What classic test of cognitive ability in children did Sarah the chimp pass?

Woodruff and colleagues (1978) showed that Sarah, an adult chimpanzee, could pass some of the tests developed for human children by the Swiss psychologist Jean Piaget. Piaget is famous for his demonstration that small children cannot keep track of concepts like liquid quantity. If you fill a narrow beaker full of colored water, a young child will assume it has "more" in it than the beaker next to it which is twice as fat but has a slightly lower level of liquid. Around the age of 5, children become able to pass Piaget's test. They come to realize that the amount of liquid does not change just because it is in a differently shaped container. Sarah the chimp could pass this type of test, too.


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Copyright © 2007 Russ Dewey