"You can't ask What does it mean?" Maestripieri said. "It doesn't mean anything. It's the intonation that matters."
But the sounds appear to serve a key purpose.
"They don't have a meaning linked to a representation of an item or object, but they may perform a very important social function to bring individuals together," said Lisa Parr of Yerkes National Primate Center at Atlanta's Emory University. Parr was unaffiliated with the research.
For instance, adult females use motherese to speak to infants other than their own.
This makes the infants' mothers more receptive to social overtures, such as grooming. It also promotes social interaction among the group's females. (Related: "Monkeys Hug to Head Off Conflict, Study Finds" [March 2, 2007].)
Though it may seem odd that monkey moms don't use motherese on their own offspring, it may be that they simply don't need to.
"Moms carry their own infants on their chest almost all the time," study co-author Maestripieri said.
"So [their babies] are not as novel to them as they are to other females. They also don't need to do anything special to get their attention because they are almost constantly face-to-face."
Parr said the study is one of the first of its kind.
"In terms of auditory signals this may be one of the first articles that speaks directly to the verbal communication between adults and infants," Parr said.
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