"Embraces in spider monkeys appear to be a method of reassuring the recipient of benign intent and reducing tension," Slater explained. "Embracing is a potentially risky behavior, as it exposes vulnerable parts of the body, such as the shoulders, face and neck, and is therefore an honest signal to the mother that the (hugger) does not intend to harm her or her baby."
Mothers approached by females who did not offer a hug protectively snubbed the curious females by either turning their bodies to create a physical barrier, or by moving — baby in tow — away from the approaching individual.
Louise Barrett, a researcher in the Evolutionary Psychology and Behavioral Ecology Research Group at the University of Liverpool, previously found that female baboons engage in similar behavior, only they exchange grooming for baby handling.
Barrett told Discovery News that at first she wondered how anyone could make a similar finding about spider monkeys, which do not spend much time socially grooming.
"The fact that embraces function in the same way (as grooming) — and perhaps more effectively — is interesting," Barrett said.
Slater believes the "biological market," whereby individuals exchange either grooming or hugs for baby time, may illustrate the origins of human hugging.
She explained that spider monkeys live in the same type of societies as chimpanzees do. Since chimp societies are, in turn, similar to human societies, "it is therefore possible to make direct links between spider monkey social behavior and the evolution of human social behavior."
Related Links:
Love Signals: A Practical Field Guide to the Body Language of Courtship
Honolulu Zoo page on spider monkeys.
Spider monkey conservation in South America
Carl Zimmer's musings on life, past and future.
