Monkey see, monkey coo.
Rhesus monkeys use baby talk with infants.

Amanda Accamando/Louisiana State University

Making Sense of Baby Talk

There may be more to baby talk than cooing over cuteness. A new study suggests that female rhesus monkeys engage in a kind of baby talk, casting doubt on the long-held belief that the behavior is exclusively human. And another study--in humans--shows that the tones mothers use to address their children may be universal.

Although female rhesus monkeys don't baby talk to their own young, they make pantlike grunts and high-pitched, melodic nasal sounds called girneys when near other baby monkeys. Scientists assumed the females were "talking" to other mothers, not the infants, as a way of showing they had no ill intent toward the youngsters.

Jessica Whitham, who is now an animal behaviorist at Brookfield Zoo near Chicago, Illinois, wasn't so sure the mothers were the intended audience. So she and University of Chicago behavioral biologist Dario Maestripieri spent 2 years observing wild monkeys on the Puerto Rican island of Cayo Santiago. They watched 19 female rhesus monkeys both before and after their birth season. They found that whereas grunts and girneys were rare before the birth season, they "just exploded" once the first infants appeared. When infants briefly wandered away from their mothers, the other females kept a close eye on them and grunted or girneyed, and the infants frequently looked back at them, which led Whitham and Maestripieri to conclude that the sounds are meant to attract the infants, not the mothers.

In that sense, rhesus monkeys use baby talk just like we do, the team reports in the September issue of Ethology. Drew Rendall, an animal behaviorist at the University of Lethbridge in Canada, agrees that the sounds resemble baby talk--particularly because they may not have meaning. "The vocalizations themselves have a soothing quality that calms mothers and infants, which makes it more like human baby talk," he says. But Rendall isn't convinced the baby talk is really directed at the infants. "It's hard to tell who the audience is when the infants and mothers are generally so close together," he says. Joan Silk, a primatologist at the University of California, Los Angeles (UCLA), says that follow-up experiments under more controlled conditions are needed.

Meanwhile, researchers are learning a bit more about a close relative of baby talk, "motherese." UCLA evolutionary psychologists Gregory Bryant and H. Clark Barrett recorded American moms addressing their children in approving or disapproving ways--saying things such as, "You did a good job" or "Don't touch that!" They also recorded the moms saying similar things to adults. The researchers then played the recordings to indigenous Shuar villagers in remote Ecuador.

Despite not speaking English, the Shuar could tell whether the speaker was addressing an adult or a child 73% of the time, and they correctly gauged the tone as approving or disapproving 75% of the time. The study, which appears in the August issue of Psychological Science, is the first to show that listeners can distinguish between motherese and adult talk across cultural and language barriers.

Bryant sees a parallel between the rhesus and human studies. "Motherese is actually closer to animal communication than people realize," he says, because the tone of the speech and the response it elicits can be just as important as its content. Bryant predicts that future animal-communication studies will turn up more versions of "motherese" across a wide range of species. "If we look close enough," he says, "we'll see it."

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