Motherese

September 2007 - New research by Jessica Whitham and Dario Maestripieri from the University of Chicago and Melissa Gerald from the University of Puerto Rico published in Ethology has found that female rhesus monkeys use particular vocalizations while interacting with their babies comparable to the way humans use "motherese" or "baby talk". However, the study also found that contrary to human experience, rhesus macaques did not direct these calls toward their own offspring. Researchers speculate that monkey mothers are familiar with their own babies and may vocalize when excited about seeing a new infant.

Dario Maestripieri, associate professor in comparative human development explained:

"Motherese is a high pitched and musical form of speech, which may be biological in origin. The acoustic structure of particular monkey vocalizations called girneys may be adaptively designed to attract young infants and engage their attention, similar to how the acoustic structure of human motherese, or baby talk, allows adults to visually or socially engage with infants."

Researchers studied a group of free-ranging rhesus macaques living on an island off the Puerto Rican coast and found that grunts and girneys exchanged by adult females increased dramatically in the presence of a baby and when a baby wandered away from its mother other females looked intently at it and vocalized.

Lead author and recent Ph.D. graduate Jessica Whitham commented:

"Adult females become highly aroused while observing the infants of other group members."

The authors explain that there has been extensive research into the noises made by non-human primates and how these contribute to communication. In the current study:

"The calls appear to be used to elicit infants' attention and encourage their behavior. They also have the effect of increasing social tolerance in the mother and facilitating the interactions between females with babies in general. Thus, the attraction to other females' infants results in a relatively relaxed context of interaction where the main focus of attention is the baby."

The authors suggest that monkey vocalizations may transmit information that the sender expects to be specifically understood or they could be noises that the recipient can draw inferences from. They compare a human sneeze that people understand may be associated with a cold, but that was evolved for reasons other than to convey this information.

Researchers suggest that adult monkeys in the current study emitted grunts and girneys to attract attention or change their emotional states rather than convey specific information. However, when females vocalize to young infants their mothers infer that the motive is playful and harmless. These vocalizations may contribute to social cohesion by facilitating interaction between adult females; the grunts and girneys sometimes being followed by an approach and grooming.