full story, photos:
March 5, 2013
When does a monkey turn down a free treat? When it is offered by a
selfish person, apparently.
Given the choice between accepting
goodies from helpful, neutral or unhelpful people, capuchin monkeys (Cebus
apella) tend to avoid individuals who refuse aid to others, according to a
study published today in Nature Communications 1.
"Humans can build up an impression about somebody just based on what we
see," says author James Anderson, a comparative psychologist at the
University of Stirling, UK. The capuchin results suggest that this skill
"probably extends to other species", he says.
Anderson chose to study
capuchins because of their highly social and cooperative instincts. Monkeys
in the study watched as a person either agreed or refused to help another
person to open a jar containing a toy. Afterwards, both people offered a
food pellet to the animal. The monkey was allowed to accept food from only
When help was given, the capuchins showed little preference between the
person requesting help and the one providing aid. But when help was denied,
the seven monkeys tended to accept food less often from the unhelpful person
than from the requester.
To try to understand
the monkeys' motivations, Anderson and his team tested different scenarios.
The animals showed no bias against people who failed to help because they
were busy opening their own jar. But they tended to avoid people who were
available to help but did not do so.
"Explicit refusal to help is a
signal that you're dangerous, that you're negative," says Kiley Hamlin, a
developmental psychologist at the University of British Columbia in
Vancouver, Canada. Similar biases have been shown in chimpanzees
2 and in 3-month-old humans 3. Hamlin
says that the capuchin study suggests that being able to identify
undesirable social partners has ancient evolutionary roots.
Brosnan, an ethologist at Georgia State University in Atlanta, says that
this type of study is usually done with great apes and "it's really
interesting to see this in a monkey". The findings suggest that social
inference may occur in animals that vary widely in brain size and cognitive
ability, she explains.
But Jennifer Vonk, a comparative psychologist
at Oakland University in Rochester, Michigan, and an author of the
chimpanzee study, cautions against assuming that the monkeys understand much
about human character.
"You really don't know what they're
inferring," she says. In conditions in which both people were given jars,
the biases against unhelpful people were weaker, she explains, so stronger
tests are needed to rule out possible preferences of the monkeys for people
who control objects of interest, such as toys.
Still, Vonk says that
she is interested in seeing whether other social animals -- dogs, for
instance -- and even non-social species, such as bears, guide their
behaviour by watching social interactions.
1 Anderson, J. R.,
Kuroshima, H., Takimoto, A. & Fujita, K. Nature Commun.
Subiaul, F., Vonk, J., Okamoto-Barth, S. & Barth, J. Anim. Cogn. 11, 611�623
3 Hamlin, J. K., Wynn, K. & Bloom, P.
Nature 450, 557�559 (2007).