The high-pitched, exaggerated “goo-goo gah-gahs” adults use only when talking to babies may have originated in our transition from four legs to two, suggests an anthropologist at Florida State University in Tallahassee.

According to Dr. Dean Falk, human mothers and babies greatly resemble chimpanzee mothers and babies in almost all respects, except one: chimps do not use babytalk with their infants. They tickle their infants like we do, interact with them in a similar way, but they are relatively “silent,” she told AMN Health.

To investigate why, Falk reviewed recent research conducted on chimp mother-child pairs, and humans, and the phenomenon of babytalk.

She found that chimp babies are born much more developed than human babies. Once they reach their two-month birthday, for instance, chimps can cling independently to their mothers, and nurse whenever they want, Falk explained. “That baby is glued to her body, and she can go about her business,” she said.

When humans evolved from chimps, she noted, we began walking upright, which caused women’s hips to narrow. Our babies also developed bigger heads, to accommodate our bigger brains.

The only solution to the pelvis-head size problem was for women to give birth to babies at a relatively early stage in development, when they are much more dependent than little chimps, she said.

“We have little unfinished babies with big heads,” Falk noted, adding that childbirth is still much more painful for humans than chimpanzees.

Babytalk likely became important during this transition from chimps to humans, Falk argues.

Since early human mothers had to hold babies themselves, there must have been times - before slings, backpacks and other carriers - when mothers had to put babies down. During those moments, speaking to babies in a soothing way helped reassure them, and maintained their link to their mothers, the researcher writes in the journal Behavioral and Brain Sciences.

And when humans created language, babytalk picked up another purpose, by exposing babies to words early in life and enabling them to start talking themselves, she added.

So why do adults use that sing-song voice to speak to babies? Previous research has examined that question, Falk noted, and found that babies prefer to hear high-pitched, exaggerated words. Even deaf babies appear to prefer exaggerated forms of sign language over normal signing, she added.

SOURCE: Behavioral and Brain Sciences.