Baby talk may explain what sets humans apart from apes

Child-directed speech, also known as “baby talk,” plays a vital role in human development. Around the world, caregivers use a distinct vocal style to talk to infants.

These modified speech patterns help young minds absorb vocabulary and structure. But how did this behavior originate? Could it have evolved from our primate ancestors?

A recent study led by researchers from the University of Zurich, University of Neuchâtel, and collaborators across Europe and the U.S. offers new insights.

The research, published in the journal Science Advances, explores whether great apes use infant-directed vocalizations like humans do.

Baby talk in humans and apes

The team observed wild populations of bonobos, chimpanzees, gorillas, and orangutans. They also included data from human infants across diverse cultures: Shipibo-Konibo, Qaqet, Chintang, and Tuatschin.

To quantify communication, they analyzed vocal behavior during two-minute intervals. They categorized each instance as infant-directed, surrounding, or general vocal activity.

They followed immature individuals closely, noting all relevant sounds from nearby group members.

Humans use baby talk way more

These results highlight how unique human caregiving behavior is compared to that of our closest relatives. Human infants are surrounded by vocal input that is not only frequent but also specifically tailored to them. This level of attention likely helps them learn language faster and more efficiently.

Even when focusing only on what mothers said, humans stood out. Mothers spoke directly to their babies far more than ape mothers did. In fact, the difference between human and bonobo mothers was over 400-fold.

Most of the speech around human infants was directed at them. In contrast, great apes showed almost no such targeted communication.

This suggests that humans may have evolved a special way of teaching language that relies heavily on speaking directly to infants.

Not just direct speech

Surrounding speech refers to vocalizations that infants can hear but are not directly addressed to them. This type of input was fairly consistent across humans, chimpanzees, and bonobos.

These species likely live in more socially active environments, where infants overhear conversations or calls.

Orangutans, however, received much less surrounding speech. This fits their more solitary lifestyle, where fewer individuals are nearby to produce vocalizations.

Because infant-directed speech is rare among apes, they may depend more on what they hear in the background. This ambient input could help them learn communication patterns, even without being directly taught.

Baby talk helped humans evolve

The data suggest a sharp evolutionary shift. “Our findings suggest that the tendency to direct vocalizations at infants… has been massively expanded in the human lineage,” the authors wrote.

One possible driver is the need to transmit learned communication. Unlike apes, human language is highly flexible and requires teaching. Infant-directed speech helps children grasp words, tone, and context more easily.

Interestingly, gestures may play a more prominent role in great apes. Repetitive gestures in apes mirror some features of human baby talk. These findings hint that vocal and gestural teaching modes may have evolved in parallel.

Are humans alone? Not quite

Other species also engage in infant-directed communication. Dolphins change pitch when around calves. Bats alter calls to suit pups. Cats and monkeys use specific sounds to call or calm infants.

However, these communications likely serve different functions, like identification or retrieval. Only in humans do these vocal patterns appear tightly linked to complex language learning.

Studying apes to understand ourselves

The study opens up new paths. The researchers propose exploring who produces surrounding speech in ape societies, siblings, mothers, or others, and whether that affects learning.

Additionally, they call for deeper study of ape gestures directed at infants. “The gestural modality might represent an additional fruitful avenue for future work.”

This research provides strong support that child-directed speech may have evolved to support language learning. Our ancestors likely began with ambient communication, then shifted toward more intentional, tailored speech as language grew more complex.

By comparing the way species talk, or don’t talk, to their young, we gain a clearer view of what makes human language so powerful and so unique.

The study is published in the journal Science Advances.

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