Chimp Study: Only Humans Are Spiteful

Chimp Study: Only Humans Are Spiteful

Jennifer Viegas, Discovery News

July 16, 2007 — A new study on our closest living relatives,
chimpanzees, found the animals might enact revenge under certain
circumstances, but never with spite.

The finding, published in the latest Proceedings of the National
Academy of Science, suggests homo sapiens are the only known species
that sometimes feel a need to see others suffer.



For chimps, on the other hand, the message is, "Don't mess with my lunch, or else."



Researchers Keith Jensen, Josep Call and Michael Tomasello of the Max
Planck Institute for Evolutionary Anthropology in Germany devised
experiments where 13 chimps could pull a string attached to a table,
causing the table to collapse and fall to the ground. The primates had
no trouble doing this, and quickly learned not to pull the string when
they were eating food that was resting on the table.



A few study phases tested the general frustration of chimps, since the
scientists would allow one chimp to dine in front of another. The
onlooker could not reach the food, yet could pull the string. In
another version of this test, a person would grab food from one eating,
potentially string-pulling chimp and then give the food to another in
full view.



The only situation that repeatedly caused the chimps to collapse the
table was when a chimpanzee would blatantly steal food from the other.
The victim would then pull the string, but without pleasure.



"The chimpanzees who collapsed the table were often angry and would
continue to threaten the thief," lead author Jensen told Discovery
News. "If they had the chance, and they were dominant, they would
likely have beaten up the other chimpanzee."



The chimps did not seem to hold a lasting grudge, however.



Jensen said "when the test was done and the subjects were allowed to be
with the rest of the group, there appeared to be no consequences for
either individual."



The researchers believe punishment — in this case disrupting lunch —
can benefit social groups in the long run, since it may discourage
selfish behavior and help prevent "the degrading influence of
free-riders."



Spite, on the other hand, is not always a means to an end, but rather is an end in itself.



A sneaky human, for example, might hide and pull on the string just to
enjoy seeing the table collapse underneath someone else whose lunch was
on the table.



Jensen said such spitefulness "is the evil twin of altruism." Just as
an empathetic person may help someone even when the only reward is
feeling good about the charitable act, a spiteful individual could hurt
another even when the only reward is enjoying, or gaining satisfaction
from, the other's suffering.

Jensen therefore thinks spitefulness "may form the basis of altruistic
punishment, which is a key component for the maintenance of cooperation
in groups."



Although the jury is still out on whether non-human primates exhibit
altruism, Danielle Stith, primate keeper at the Oakland Zoo in
California, has observed that for chimps, "you scratch my back and I'll
scratch yours" is literally true.



"I've seen chimps whimper for food that another chimp is eating," Stith
told Discovery News. "After a period of this, the eating chimp will
often share, probably because it knows that somewhere down the line,
such as during mutual grooming sessions, it may need this other
individual's help."



Lower primates, like baboons and monkeys, are not nearly as
cooperative. She said dominant male and female baboons may just "push
others away," while monkeys might think nothing of taking a bite out of
someone else's food.



While differences clearly exist between higher and lower primates, some
discrepancies in social behavior between humans and chimpanzees are
less clear.



Jensen and his team are now studying whether or not chimps can
recognize "nice" and "nasty" human experimenters, based on how the
humans treat the animals. They are also investigating how chimps may
punish thieves, even when the potential punishers did not directly
suffer the losses.