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The evolution and economics of human relationships.

What Monkeys Can Teach Us About Human Behavior: From Facts to Fiction

When creativity crosses the line

In a 2011 PT blog post called "What Monkeys Can Teach Us About Human Behavior", Michael Michalko (MM) described an experiment involving five monkeys, a ladder, and a banana. Descriptions of this experiment can also be found on the Internet, as a result of this story being told many times in various blogs, books and speeches. The experiment as described in the story, however, never happened.

This is how MM described the experiment in his blog post. "This human behavior of not challenging assumptions reminds me of an experiment psychologists performed years ago. They started with a cage containing five monkeys. Inside the cage, they hung a banana on a string with a set of stairs placed under it. Before long, a monkey went to the stairs and started to climb towards the banana. As soon as he started up the stairs, the psychologists sprayed all of the other monkeys with ice cold water. After a while, another monkey made an attempt to obtain the banana.  As soon as his foot touched the stairs, all of the other monkeys were sprayed with ice cold water. It's wasn't long before all of the other monkeys would physically prevent any monkey from climbing the stairs. Now, the psychologists shut off the cold water, removed one monkey from the cage and replaced it with a new one. The new monkey saw the banana and started to climb the stairs. To his surprise and horror, all of the other monkeys attacked him.  After another attempt and attack, he discovered that if he tried to climb the stairs, he would be assaulted. Next they removed another of the original five monkeys and replaced it with a new one. The newcomer went to the stairs and was attacked. The previous newcomer took part in the punishment with enthusiasm! Likewise, they replaced a third original monkey with a new one, then a fourth, then the fifth. Every time the newest monkey tried to climb the stairs, he was attacked. The monkeys had no idea why they were not permitted to climb the stairs or why they were beating any monkey that tried. After replacing all the original monkeys, none of the remaining monkeys had ever been sprayed with cold water. Nevertheless, no monkey ever again approached the stairs to try for the banana. Why not? Because as far as they know that's the way it's always been around here." MM then concludes: "People sometimes do the same in the workplace. How many times have you heard "It has always been done this way. Don't mess with what works." Instead of challenging these assumptions, many of us, like the monkeys, simply keep reproducing what has been done before. It's the easiest thing to do."

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In a comment to MM's blog post, primatologist Frans De Waal expressed some skepticism about the experiment and asked MM if he had a scientific reference for this study. In response to the comment from another reader, MM posted the following response: "FIVE MONKEYS. This story originated with the research of G.R. Stephenson. (Stephenson, G. R. (1967). Cultural acquisition of a specific learned response among rhesus monkeys. In: Starek, D., Schneider, R., and Kuhn, H. J. (eds.), Progress in Primatology, Stuttgart: Fischer, pp. 279-288.)
Stephenson (1967) trained adult male and female rhesus monkeys to avoid manipulating an object and then placed individual naïve animals in a cage with a trained individual of the same age and sex and the object in question. In one case, a trained male actually pulled his naïve partner away from the previously punished manipulandum during their period of interaction, whereas the other two trained males exhibited what were described as "threat facial expressions while in a fear posture" when a naïve animal approached the manipulandum. When placed alone in the cage with the novel object, naïve males that had been paired with trained males showed greatly reduced manipulation of the training object in comparison with controls. Unfortunately, training and testing were not carried out using a discrimination procedure so the nature of the transmitted information cannot be determined, but the data are of considerable interest.
His research inspired the story of five monkeys. Some believe the story is true, while others believed it's an exaggerated account of his research. True story or not, his published research with rhesus monkeys, in my opinion, makes the point."

So MM apparently knew that the Stephenson's study did not involve a ladder or a banana (this aspect of the story is inspired by experiments with chimpanzees conducted by Wolfgang Kohler in the 1920s), that the monkeys were not replaced in the group they way he described it in the story, that the monkeys did not attack the individual who tried to climb the ladder (let alone that they "..took part in the punishment with enthusiasm!"), and that in the end no monkey ever again approached the stairs to try for the banana "because as far as they know that's the way it's always been around here."  As for MM's last comment "true story or not, his published research with rhesus monkeys, in my opinion, makes the point", I couldn't disagree more. Whether or not the story of the experiment is true makes a big difference. When people report scientific experiments in books or blogs, the readers expect these reports to be true. If an author wants to make up a story to make a point, he should explicitly tell the reader that the story was invented. If the author is unsure as to whether a story is true, he should check his sources or at least warn the readers that the description of the experiment may be inaccurate. In this case, it appears that MM had the original source of the study and knew that it didn't match his description. The real experiment didn't even make the point that MM wanted to make, that "monkeys simply keep reproducing what has been done before because it's the easiest thing to do."

Stephenson's experiment was a study of learned fear conditioning in which various objects (conditioned stimuli, CS) were paired with an airblast (the unconditioned stimulus, US). After the conditioning occurred, a male observer was placed in the same enclosure as the model, giving the observer the opportunity to watch the model behave fearfully in the presence of the object. During subsequent testing in isolation, 3 of the 4 observers exhibited fear of the object, suggesting that they had learned to fear the object from the behavior of the model. In reviewing Stephenson's study, psychologist Susan Mineka noted that when female subjects were used, Stephenson found opposite results: previously fearful models lost their fear as a result of watching the nonfearful behavior of their observers. Mineka noted that "...regardless of its cause, this [sex difference] raises serious questions about the robustness of the phenomenon." Studies conducted by Susan Mineka herself demonstrated that if a snake is used as the conditioned stimulus, fear can be learned from observing the behavior of a model, but this association does not occur if other objects such as kitchen utensils are used.

I asked Dr. Bennett (Jeff) Galef, a comparative psychologist who is an expert in animal social learning to comment on the experiment described by MM.  He answered "...it strikes me as very unlikely that, in the 1960s, someone with Stephenson's limited ability as an experimentalist could have conceived of, adequately designed or successfully completed an experiment of the sophistication of that in the story you describe. The story reflects a combination of Kohler's work with chimps, Jacob and Cambell's (1961) work with humans, and Curio and Mineka's work with respectively European blackbirds and monkeys. To my knowledge, no two of these elements were combined in a single experimental paradigm until 1995."

I don't know if the fictionalized version of the Stephenson study was created by a single person or whether every time the story was re-told by a different person, some aspect of it was changed, added, or removed, the way it happens with legends. But whatever the process was, there was a lot of Creative Thinkering involved!

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Dario Maestripieri, Ph.D., is a professor of comparative human development, evolutionary biology, and neurobiology at the University of Chicago.

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