Babbling brains: How human babies and marmosets learn to talk

Every parent delights in a baby’s babbling, those streams of sounds that fill the air. To the untrained ear, it may seem like sweet but meaningless noise. In reality, these exchanges shape the foundation of human language.

When parents respond to babbling, babies begin linking their vocal efforts with feedback, gradually refining the sounds that will form words.

This style of learning, however, sets humans apart in the animal world. Few creatures, aside from certain songbirds, rely on this feedback-based learning to acquire communication skills. The puzzle deepens when we consider our primate relatives.

A babbling path to language learning

Chimpanzees and macaques can produce their species’ calls with minimal guidance. So why do humans, and intriguingly, a tiny monkey called the marmoset, share this unusual developmental path, relying so heavily on feedback and interaction during infancy?

This surprising overlap suggests that unique pressures in their environments may have shaped similar strategies, raising fresh questions about how evolution repeatedly crafts pathways to complex communication.

Babbling marmoset monkeys

In Brazil’s dense forests, marmosets keep in touch using high-pitched calls. Princeton neuroscientist Asif Ghazanfar first noticed that infant marmosets babble like human babies, experimenting with sounds before mastering adult calls.

As adults responded to these vocal attempts, the young monkeys learned faster. “That was a pretty big ‘aha!’ moment,” Ghazanfar said. The discovery, reported in 2015 and 2017, was among the earliest evidence of vocal learning in a primate outside humans.

Yet humans and marmosets diverged evolutionarily some 40 million years ago. Even chimpanzees, our closest cousins, require little tutoring to develop their species-specific sounds.

“So that kind of presents a puzzle,” Ghazanfar said. Researchers have since searched for answers hidden in early development.

Brains growing fast

A recent study led by Princeton Ph.D. student Renata Biazzi examined brain growth across humans, marmosets, chimpanzees, and macaques.

The team analyzed developmental data from conception through adolescence. The results showed that both human and marmoset brains grow at a remarkable pace right after birth.

This timing matters. For chimpanzees and macaques, most neural growth occurs before birth, limiting postnatal influence. But for marmosets and humans, the brain expands rapidly during infancy, when social interaction is intense.

Social environment and learning

Marmoset mothers, like human parents, do not raise infants alone. Babies experience constant responses from multiple caregivers. “They are a handful,” Ghazanfar said.

Because their brains are still developing, that means that the social environment an infant is born into has a tremendous influence on learning, noted Ghazanfar.

With modeling, the researchers showed how this blend of fast brain growth and caregiver interaction fuels vocal skill development.

Feedback-driven learning in songbirds

Interestingly, similar feedback-based learning also appears in certain bird species. Songbirds like zebra finches and cowbirds mimic adult calls while refining their own songs.

Just as baby marmosets depend on adult responses, young birds adjust their notes based on social cues.

The parallel suggests that feedback-driven learning may evolve in species where communication plays a central role in survival and bonding, influencing not only group cohesion but also mate selection and territorial defense.

Development of complex communication

In many cases, birds that master songs more effectively enjoy greater success in attracting mates and maintaining social standing within flocks.

This pattern hints that vocal learning shaped by feedback is not an isolated curiosity, but a broader strategy favored by evolution whenever social life and communication are tightly interwoven.

This cross-species echo raises a bigger question: did such strategies emerge independently, or do they reveal deeper evolutionary patterns guiding the development of complex communication across distant branches of life?

Learning language through babbling

The next question is whether marmoset adults use distinct sounds when addressing infants.

Humans instinctively shift into “baby talk,” exaggerating pitch and rhythm. If marmosets do something similar, scientists may gain new insights into how children progress from babbling to speaking fluently.

This does not suggest other primates cannot adapt their calls later. But the special window of infancy may be key. “We’re only talking about vocal learning during infancy,” Ghazanfar said. “This is the period when their brains are especially malleable.”

By studying marmosets, researchers can better understand why humans developed this rare learning style and how our earliest vocalizations connect to one of humanity’s most defining abilities: language.

The findings highlight how fragile and powerful the link between biology and environment can be, and why understanding these connections may shed light on how communication first shaped human culture.

The study is published in the journal Proceedings of the National Academy of Sciences.

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