Sounds wacky, but:
"...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."
They sound very social: ""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 researchers' hypothesis: "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."
Regardless, the monkey pic is adorable, and I'm always happy to find more data supporting the positive effects of physical contact with other beings.