From Science:
We all do it: Give friends and family a peck on the cheek, a quick hug, or maybe even a nose rub to say hello. It’s a way of assuring each other that we have no hostile intent, anthropologists say. Now, primatologists report that spider monkeys embrace intensely after a period of separation for exactly the same reason.
Like humans and chimpanzees, spider monkeys (Ateles geoffroyi) live in small groups that split apart to feed or hunt (or shop at Saks) and then rejoin later in the day. For years, researchers have noticed that these monkey reunions are often accompanied by public displays of hugging. “They give a quick call and look intensely at each other, and then briefly wrap each other in their long arms in what’s almost a passionate embrace,” says Filippo Aureli, a primatologist at Liverpool John Moores University in the U.K. In some cases, the monkeys even curl their tails around one other.
More here.