friend. John Mitani, a behavioral ecologist who has been observing chimpanzees in Uganda’s Kibale National Park
since the mid-1990s, says his studies
show general patterns in who sides
with whom.
“When male chimps form coalitions,
they take sides, but they don’t do so ran-
domly,” says Mitani, of the University of
But people, and perhaps other animals,
make friends for another reason too:
Because it feels good. Sharing time with
a friend is not only relaxing, but it can
also have a positive effect on health and
well-being.
Michigan in Ann Arbor. “They take sides
with individuals who
will later turn around
and help them.”
Though it’s difficult to assess exactly
why one critter is helping another, sci-
entists are finding ways to sort this out.
Such alliances are
formed around the
idea “you scratch my
back and I’ll scratch
yours,” rather than
kinship, he says. In
2009, Mitani showed
that 22 of 28 male
chimps in a single
group formed their
longest, closest bond
with an unrelated
animal, with some
friendships lasting a
decade or more.
One way to “interview”
an animal is by looking
at its hormonal profile,
to see what is upsetting
and what causes delight.
Familiarity and reward
1.0
0.8
0.6
0.4
Zoologist Elissa
Cameron of the University of Pretoria
in South Africa has
found similar behavior among wild, unrelated female horses
in New Zealand: The
mares form long-term alliances, in part
to keep aggressive
stallions at bay.
Vicarious reinforcement index
0.2
Catherine Crockford
of the University of St.
Andrews in Scotland,
who studies chimpanzees in Uganda’s
Budongo Forest, is looking for hormonal links
related to stress or social
bonding in the chimps
as they engage in various
behaviors with others.
Moscovice is also using
this approach to study
wild female bonobos.
By looking at how levels of certain hormones,
such as oxytocin, change
as the animals go about
their routine business,
the researchers hope to
pinpoint interactions
that promote social
bonds.
The fact that an
animal would risk injury on behalf
of another, even though they are not
related, suggests that these friendships
are extremely important to the animals,
Moscovice says.
In a recent book, Friendship: Development, Ecology, and Evolution of a
Relationship, anthropologist Daniel
Hruschka of Arizona State University in
Tempe argues that human friendships
offer an evolutionary advantage because
people can’t always get what they need
from their kin.
Oxytocin is best known
for its role in childbirth
and breast-feeding and
its promotion of mother-infant attachment. But oxytocin is also secreted during other forms of pleasant touch, such
as massage or sex, and has been shown
to stimulate bonding in animals such as
prairie voles. Though scientists have yet
to figure out how oxytocin fosters bonding, studies show that it promotes feelings
of relaxation and well-being, and serves
to enhance behaviors that reflect trust
and generosity in humans.
In a series of experiments, Duke University neuroscientist Michael Platt
0
Familiarity between
donor and recipient
More familiar Less familiar
Rewarding a friend
In an experimental setup, rhesus
macaques were more likely to
deliver a juice reward to a second
monkey if the two saw each other
frequently. A higher vicarious reinforcement index indicates more
rewards.
showed that oxytocin may promote generosity in monkeys as well. Platt’s team
trained a group of rhesus macaques to
associate certain colored shapes on a
computer screen with either a reward
to self, a reward to another monkey or
no reward at all. Last year, the scientists showed that, when given a choice
between rewarding someone else or giving no reward at all, monkeys choose to
reward the other more frequently if the
recipient was seen on a day-to-day basis.
In an experiment reported in January
in Proceedings of the National Academy
of Sciences, the scientists found that a
male monkey given a whiff of oxytocin
became increasingly generous with
his rewards to others, even if he wasn’t
chummy with them. In both experiments, the scientists also tracked the
monkeys’ gaze, to see where their attention was focused. Reward-giving monkeys spent more time gazing at the face
of the recipient immediately after sending the juice reward. Platt says the findings suggest that observing a monkey
receiving a reward may bring some kind
of vicarious reward back to the giver.
The scientists now plan to expand their
studies, looking at the neural circuits
involved in reward-related brain activity in the animals. Such work may help
reveal whether giving another monkey
a reward creates a positive experience
similar to receiving one. If so, the findings
may point to neural wiring that promotes
social bonding and altruistic behavior.
Facebook for animals
Vicarious rewards aside, some individuals are natural social networkers, while
others are not. In her book Baboon
Metaphysics, Cheney relays the story
of Ruby, a young, low-ranking but gregarious baboon who lost all her kin in a
leopard attack. Because kin are the lifeblood of social support in female baboon
society, a low-ranker such as Ruby might
be left with little access to food and other
resources.
Despite lacking the skill to set up a
Twitter account, likable Ruby managed
to build a network of followers by taking
advantage of her social opportunities.
KATHMANDUPHOTOG/SHUTTERSTOCK
www.sciencenews.org
