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Baby Talk May Be Biological in Origin

Posted on: Friday, 24 August 2007, 00:15 CDT

CHICAGO -- Adult rhesus macaques make high-pitched, sing-songy vocalizations when they encounter infant monkeys _ just the kind of sounds humans seem to naturally fall into using around infants, scientists reported this week.

Seeing the adult monkeys use a form of baby talk suggests the behavior in humans may be biological in origin, said Dario Maestripieri, associate professor of comparative human development at the University of Chicago.

In monkeys the vocalizations are called "girneys," and they are a sound completely different from any other the animal makes, said Maestripieri.

"It's a very strange sound," he said, "made with their mouths almost closed, sort of nasal and relatively soft. I can't replicate it, but it is used almost exclusively when adult monkeys see babies."

Previous studies by other scientists had concluded that when a rhesus monkey approached a mother and its baby, it directed the girney vocalization at the mother to signal the caller's intentions were benign and harmless _ that it was not threatening mother or child.

But after watching 19 adult females in a family of 65 rhesus monkeys on the Puerto Rican island of Cayo Santiago daily for months at a time, co-author Jessica Whitham said she saw something quite different was happening.

"Actually, they are looking at the baby when they are producing these vocalizations, so we think they are intended for the baby, not the mother," said Whitham, a recent Ph.D. student of Maestripieri's. "They also mix in grunt vocalizations, but the girney may be more similar to baby talk, an acoustic structure intentionally designed to attract attention of the infant."

The intent seemed simply to get the infant to look over and make eye contact with the caller, she said, then to amuse the infant, much as a human might try to get a baby to smile.

A rhesus macaque wanting to charm a tot has an advantage over a human: Besides babbling in baby tongues, it can wag its tail. The monkeys often wag their tails in the presence of a monkey infant, like a human using a rattle to entertain the little one.

Maestripieri and Whitham published a paper on their findings Friday in the research journal Ethology, based on observations made with a third co-author, Melissa Gerald of the University of Puerto Rico, in 2004 and 2005 of free-ranging families of rhesus macaques living on the island.

The girney sound "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," Maestripieri said.

The use of baby talk by the monkeys differs dramatically from human baby talk in some respects. For one, only adult female monkeys use the girney vocalization. Male rhesus monkeys have never been observed using it, but they also take virtually no part in rearing the young. And monkey baby talk is associated only with monkey infants, while Whitham points out humans use it with pets and lovers as well.

Also unlike humans, monkey mothers never engage in baby talk with their own babies. It is strictly a vocalization used by females who seem to have a deep fascination for a baby belonging to another monkey, taking great pleasure when they can get the baby's attention.

"They watch the infants so intently, scratching themselves as a show of their excitement, and often wagging their tails while emitting a long string of these vocalizations," said Whitham.

Scratching themselves on the arms, legs, bellies and heads is a common monkey behavior to show excitement, said Maestripieri, but it is rare to see a monkey wag its tail.

"Tail wagging is very specific to babies," he said. "Monkeys get excited about a lot of things, like finding their favorite food, but they don't wag tails unless it is associated with seeing a baby."

Researchers are interested in vocalizations made by non-human primates and how they are used for communication, Maestripieri said.

"Both monkey and human infants have perceptual abilities that are different than those of adults," he said. "There are certain sounds that infants enjoy hearing, so adults will try to make those sounds that the baby likes to hear."

Source: Chicago Tribune

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