The #1 source for news about monkeys and apes

[Carrie McLaren <stay.free AT verizon.net>]

June 5, 2005
Monkey Business
By STEPHEN J. DUBNER and STEVEN D. LEVITT
http://www.nytimes.com/2005/06/05/magazine/05FREAK.html


Adam Smith, the founder of classical economics, was certain that 
humankind's knack for monetary exchange belonged to humankind alone. 
''Nobody ever saw a dog make a fair and deliberate exchange of one bone 
for another with another dog,'' he wrote. ''Nobody ever saw one animal 
by its gestures and natural cries signify to another, this is mine, 
that yours; I am willing to give this for that.'' But in a clean and 
spacious laboratory at Yale-New Haven Hospital, seven capuchin monkeys 
have been taught to use money, and a comparison of capuchin behavior 
and human behavior will either surprise you very much or not at all, 
depending on your view of humans.

The capuchin is a New World monkey, brown and cute, the size of a 
scrawny year-old human baby plus a long tail. ''The capuchin has a 
small brain, and it's pretty much focused on food and sex,'' says Keith 
Chen, a Yale economist who, along with Laurie Santos, a psychologist, 
is exploiting these natural desires -- well, the desire for food at 
least -- to teach the capuchins to buy grapes, apples and Jell-O. ''You 
should really think of a capuchin as a bottomless stomach of want,'' 
Chen says. ''You can feed them marshmallows all day, they'll throw up 
and then come back for more.''

When most people think of economics, they probably conjure images of 
inflation charts or currency rates rather than monkeys and 
marshmallows. But economics is increasingly being recognized as a 
science whose statistical tools can be put to work on nearly any aspect 
of modern life. That's because economics is in essence the study of 
incentives, and how people -- perhaps even monkeys -- respond to those 
incentives. A quick scan of the current literature reveals that top 
economists are studying subjects like prostitution, rock 'n' roll, 
baseball cards and media bias.

Chen proudly calls himself a behavioral economist, a member of a 
growing subtribe whose research crosses over into psychology, 
neuroscience and evolutionary biology. He began his monkey work as a 
Harvard graduate student, in concert with Marc Hauser, a psychologist. 
The Harvard monkeys were cotton-top tamarins, and the experiments with 
them concerned altruism. Two monkeys faced each other in adjoining 
cages, each equipped with a lever that would release a marshmallow into 
the other monkey's cage. The only way for one monkey to get a 
marshmallow was for the other monkey to pull its lever. So pulling the 
lever was to some degree an act of altruism, or at least of strategic 
cooperation.

The tamarins were fairly cooperative but still showed a healthy amount 
of self-interest: over repeated encounters with fellow monkeys, the 
typical tamarin pulled the lever about 40 percent of the time. Then 
Hauser and Chen heightened the drama. They conditioned one tamarin to 
always pull the lever (thus creating an altruistic stooge) and another 
to never pull the lever (thus creating a selfish jerk). The stooge and 
the jerk were then sent to play the game with the other tamarins. The 
stooge blithely pulled her lever over and over, never failing to dump a 
marshmallow into the other monkey's cage. Initially, the other monkeys 
responded in kind, pulling their own levers 50 percent of the time. But 
once they figured out that their partner was a pushover (like a parent 
who buys her kid a toy on every outing whether the kid is a saint or a 
devil), their rate of reciprocation dropped to 30 percent -- lower than 
the original average rate. The selfish jerk, meanwhile, was punished 
even worse. Once her reputation was established, whenever she was led 
into the experimenting chamber, the other tamarins ''would just go 
nuts,'' Chen recalls. ''They'd throw their feces at the wall, walk into 
the corner and sit on their hands, kind of sulk.''


Chen is a hyperverbal, sharp-dressing 29-year-old with spiky hair. The 
son of Chinese immigrants, he had an itinerant upbringing in the rural 
Midwest. As a Stanford undergraduate, he was a de facto Marxist before 
being seduced, quite accidentally, by economics. He may be the only 
economist conducting monkey experiments, which puts him at slight odds 
with his psychologist collaborators (who are more interested in 
behavior itself than in the incentives that produce the behavior) as 
well as with certain economist colleagues. ''I love interest rates, and 
I'm willing to talk about their kind of stuff all the time,'' he says, 
speaking of his fellow economists. ''But I can tell that they're biting 
their tongues when I tell them what I'm working on.''

It is sometimes unclear, even to Chen himself, exactly what he is 
working on. When he and Santos, his psychologist collaborator, began to 
teach the Yale capuchins to use money, he had no pressing research 
theme. The essential idea was to give a monkey a dollar and see what it 
did with it. The currency Chen settled on was a silver disc, one inch 
in diameter, with a hole in the middle -- ''kind of like Chinese 
money,'' he says. It took several months of rudimentary repetition to 
teach the monkeys that these tokens were valuable as a means of 
exchange for a treat and would be similarly valuable the next day. 
Having gained that understanding, a capuchin would then be presented 
with 12 tokens on a tray and have to decide how many to surrender for, 
say, Jell-O cubes versus grapes. This first step allowed each capuchin 
to reveal its preferences and to grasp the concept of budgeting.

Then Chen introduced price shocks and wealth shocks. If, for instance, 
the price of Jell-O fell (two cubes instead of one per token), would 
the capuchin buy more Jell-O and fewer grapes? The capuchins responded 
rationally to tests like this -- that is, they responded the way most 
readers of The Times would respond. In economist-speak, the capuchins 
adhered to the rules of utility maximization and price theory: when the 
price of something falls, people tend to buy more of it.

Chen next introduced a pair of gambling games and set out to determine 
which one the monkeys preferred. In the first game, the capuchin was 
given one grape and, dependent on a coin flip, either retained the 
original grape or won a bonus grape. In the second game, the capuchin 
started out owning the bonus grape and, once again dependent on a coin 
flip, either kept the two grapes or lost one. These two games are in 
fact the same gamble, with identical odds, but one is framed as a 
potential win and the other as a potential loss.

How did the capuchins react? They far preferred to take a gamble on the 
potential gain than the potential loss. This is not what an economics 
textbook would predict. The laws of economics state that these two 
gambles, because they represent such small stakes, should be treated 
equally.

So, does Chen's gambling experiment simply reveal the cognitive 
limitations of his small-brained subjects? Perhaps not. In similar 
experiments, it turns out that humans tend to make the same type of 
irrational decision at a nearly identical rate. Documenting this 
phenomenon, known as loss aversion, is what helped the psychologist 
Daniel Kahneman win a Nobel Prize in economics. The data generated by 
the capuchin monkeys, Chen says, ''make them statistically 
indistinguishable from most stock-market investors.''

But do the capuchins actually understand money? Or is Chen simply 
exploiting their endless appetites to make them perform neat tricks?

Several facts suggest the former. During a recent capuchin experiment 
that used cucumbers as treats, a research assistant happened to slice 
the cucumber into discs instead of cubes, as was typical. One capuchin 
picked up a slice, started to eat it and then ran over to a researcher 
to see if he could ''buy'' something sweeter with it. To the capuchin, 
a round slice of cucumber bore enough resemblance to Chen's silver 
tokens to seem like another piece of currency.

Then there is the stealing. Santos has observed that the monkeys never 
deliberately save any money, but they do sometimes purloin a token or 
two during an experiment. All seven monkeys live in a communal main 
chamber of about 750 cubic feet. For experiments, one capuchin at a 
time is let into a smaller testing chamber next door. Once, a capuchin 
in the testing chamber picked up an entire tray of tokens, flung them 
into the main chamber and then scurried in after them -- a combination 
jailbreak and bank heist -- which led to a chaotic scene in which the 
human researchers had to rush into the main chamber and offer food 
bribes for the tokens, a reinforcement that in effect encouraged more 
stealing.

Something else happened during that chaotic scene, something that 
convinced Chen of the monkeys' true grasp of money. Perhaps the most 
distinguishing characteristic of money, after all, is its fungibility, 
the fact that it can be used to buy not just food but anything. During 
the chaos in the monkey cage, Chen saw something out of the corner of 
his eye that he would later try to play down but in his heart of hearts 
he knew to be true. What he witnessed was probably the first observed 
exchange of money for sex in the history of monkeykind. (Further proof 
that the monkeys truly understood money: the monkey who was paid for 
sex immediately traded the token in for a grape.)

This is a sensitive subject. The capuchin lab at Yale has been built 
and maintained to make the monkeys as comfortable as possible, and 
especially to allow them to carry on in a natural state. The 
introduction of money was tricky enough; it wouldn't reflect well on 
anyone involved if the money turned the lab into a brothel. To this 
end, Chen has taken steps to ensure that future monkey sex at Yale 
occurs as nature intended it.

But these facts remain: When taught to use money, a group of capuchin 
monkeys responded quite rationally to simple incentives; responded 
irrationally to risky gambles; failed to save; stole when they could; 
used money for food and, on occasion, sex. In other words, they behaved 
a good bit like the creature that most of Chen's more traditional 
colleagues study: Homo sapiens.

Stephen J. Dubner and Steven D. Levitt are the authors of 
''Freakonomics: A Rogue Economist Explores the Hidden Side of 
Everything.''