BioEd Online

When British politician David Cameron advocated affection as a solution to antisocial behaviour and petty crime, his speech was mockingly labelled 'Hug-a-Hoodie'. But no one realized that there is a precedent in the animal kingdom — spider monkeys in Mexico have been observed embracing to avoid gang violence.

Hugging diffuses the tension when two bands of monkeys meet, say the British researchers who made the discovery. Without these calming embraces, the situation can escalate into aggression and even physical attacks, they report.

The researchers studied wild spider monkeys (Ateles geoffroyi), which live in the forests of Central and South America. These monkeys live in large groups, but split into short-lived, constantly changing groups of a few individuals to travel more easily in search of food.

"It's like the monkeys live in a small village where everyone knows each other," says Filippo Aureli of Liverpool John Moores University. "You wake up and eat breakfast with one group, such as a family, then move into different subgroups such as work, or school, and go to lunch with another group."

The small gangs bumps into one another frequently. If the other monkeys are seen as rivals, there is a danger that fighting will erupt. Hugging seems to be a way to ease the tension — aggressive encounters such as chases are more likely to happen among monkeys that do not embrace first.

Hug-happy meetings have much lower levels of aggression, Aureli and his colleague Colleen Schaffner of the University of Chester report in Biology Letters¹.

Meeting and greeting

"The embrace could be a way of testing the bond between monkeys, as it exposes vulnerable parts of the body to attack," suggests Aureli. Monkeys do not hug members of their own groups, suggesting that embraces do not just reflect general levels of affection.

Previous research has focused on how monkeys patch up their differences after a fight. But few studies have addressed whether pre-emptive peacemaking occurs in the wild, Aureli says.

Even though humans don't tend to chase or fight one another in daily life, the monkeys' hugs may be analogous to a human embrace or a handshake, Aureli argues.

He also suggests that hugging might be more important between monkeys that have not met for a few days, and are therefore unsure of the precise footing of their relationship — in much the same way as we never quite know exactly how to greet a friend we haven't seen for years.