It's
not fair!" is a
common call from the
playground and, in
subtler form, from more
adult assemblies. It now
seems that monkeys, too,
have a sense of
fairness, a conclusion
suggesting that this
feeling may be part of
the genetically
programmed social glue
that holds primate
societies together,
monkeys as well as
humans.
Two
researchers at Emory
University, Dr. Sarah F.
Brosnan and Dr. Frans B.
M. de Waal, report today
in the journal Nature
that they taught female
capuchin monkeys to
trade pebbles for pieces
of food. The capuchins
were caged in pairs, so
that each member of a
pair could see the
other. If one monkey got
a grape in return for
her pebble but the other
only a less desired
piece of cucumber, the
shortchanged monkey
would often refuse to
hand over the pebble in
exchange or might
decline to eat the
cucumber — both very
unusual behaviors.
These
refusals were often
accompanied by emphatic
body language, like
dashing the pebble or
the cucumber on the
floor, Dr. Brosnan said.
The expressions of
exasperation were twice
as common if the monkey
offered a cucumber saw
her companion being
given a grape without
even having to hand over
a pebble.
The
behavior suggests that
the monkeys have a sense
of fair treatment and
respond negatively when
their expectations are
violated, the
researchers say.
The
finding bears on the
question of whether the
sense of fairness found
in all human societies
is learned from school
and family or is instead
an innate behavior
fostered by the genes.
"The
fact that we find the
sense of fairness in a
nonhuman primate implies
it is an evolved
behavior and has a good
benefit," Dr.
Brosnan said.
Protesting
unfair treatment of
oneself, in other words,
probably has a genetic
basis in capuchins and
so presumably in all
social primates,
including people.
The
food experiment was not
conducted in male
capuchins, Dr. Brosnan
said, because they tend
to share food with
everyone, whereas
females are more
discriminate, sharing
only with those who
share with them.
The
reason stems from the
structure of capuchin
society, which is based
on a harem system. A
male shares food freely
because everyone around
is either a sexual
partner or a child he
has fathered. Females
within a harem have no
such incentive and
evidently measure out
their favors on a basis
of reciprocity.
The
monkey research is part
of a long-term effort by
evolutionary biologists
to understand the
genetic basis of social
behavior. Selfishness
might seem the best way
for an individual to get
the most genes into the
next generation,
evolution's only coin of
success. But biologists
have come to understand
how cooperative behavior,
under certain definable
conditions, can have a
greater genetic payoff
and therefore how genes
that foster such
behavior could be
favored by evolution.
The
sense of fairness
discovered in the
capuchin monkeys seems
to be another aspect of
the innate primate
repertory of social
behaviors.