A study tracking the calls of young chimpanzees at two sites thousands of kilometers apart has found that their grunts, whimpers and laughter grow more distinct from one another as the animals age. The pattern challenges a long-standing assumption that chimpanzee vocalizations are locked in by genetics alone, suggesting instead that social life and environment help shape how the animals sound.
The research, led by Queen Mary University of London doctoral researcher Kassandra Giragosian, compared infant and juvenile eastern chimpanzees (Pan troglodytes schweinfurthii) living at Chimfunshi Wildlife Orphanage in Zambia with a separate population at Gombe National Park in Tanzania. The two groups have no contact with one another, making them a useful test case for whether vocal differences between chimpanzee communities are present from birth or build up over time.
Comparing Two Chimpanzee Communities an Ocean Apart
Researchers have known for decades that adult chimpanzees in different populations produce subtly different versions of the same calls, a phenomenon some scientists have likened to regional dialects. What has remained contested is why: whether the variation comes from inherited biology, from the acoustics of each habitat, or from young animals picking up patterns from the individuals around them. To separate these possibilities, Giragosian’s team focused on the earliest stages of life rather than comparing fully grown adults, tracking how vocal patterns changed as individual chimpanzees matured.
Chimfunshi and Gombe make an especially useful pairing for that kind of comparison because the two populations are geographically separated and have no contact with one another, meaning any shared vocal traits could not spread between them through direct social contact. That separation gave the research team a natural test of whether vocal development follows a shared genetic script or instead bends toward the particular social and physical surroundings of each community.
How Grunts, Whimpers and Laughter Diverge With Age
The team analyzed recordings of grunts, whimpers and laughter from young chimpanzees at both sites, measuring acoustic features such as pitch and rhythm. Early in life, the calls from Chimfunshi and Gombe youngsters sounded broadly similar. As the animals grew older, the gap between the two populations widened, with vocal patterns becoming steadily more population-specific through infancy and into the juvenile years. That progression, the researchers wrote, provides the first direct evidence that population-level vocal differences sharpen over the course of chimpanzee development rather than existing as a fixed trait from birth.
Some Signatures Appear Early, Others Emerge Later
Not every population-specific trait followed the same timeline. The study found that certain vocal characteristics distinguishing the two groups were already detectable in infancy, while others only became apparent as the young chimpanzees entered their juvenile years. Giragosian and her colleagues described this mixed pattern as evidence that multiple influences, operating on different schedules, are shaping chimpanzee communication simultaneously rather than a single genetic switch flipping at one point in development.
Separating Genetics From Social and Ecological Influence
“Dialects are a vocal signature of population membership,” Giragosian and her co-authors wrote, noting that debate has continued over whether such signatures trace back to social learning, genetic inheritance, or the ecological conditions of a given habitat. “Early in human ontogeny, vocal behavior is relatively similar across populations from an acoustic perspective,” the team explained, before diverging “as ontogeny progresses.” Because the Chimfunshi and Gombe populations are geographically isolated with different social histories and physical surroundings, the widening vocal gap documented in the study points toward a mix of non-genetic forces, including social interaction and environmental conditions, contributing to how young chimpanzees learn to vocalize.
That interpretation runs against a simpler explanation that some researchers have favored in the past: that chimpanzee calls are essentially hardwired, with each population’s dialect fixed from birth by inherited biology alone. If that were the whole story, the researchers reasoned, differences between Chimfunshi and Gombe infants should have already been at their largest in the earliest recordings, then stayed roughly constant as the animals grew. Instead, the gap widened over time, a pattern more consistent with calls that are shaped, and reshaped, through years of exposure to a particular social group.
What the Findings Do and Do Not Show About Chimp Communication
The researchers were careful to note limits on what the results demonstrate. “Although the study does not suggest that chimpanzees possess language or human-like speech — a process that involves agreed grammar and lexicon, for instance — it convincingly demonstrates that their vocal development is influenced by more than genetics alone,” they wrote. In other words, the calls remain grunts, whimpers and laughter rather than words, but the way individual chimpanzees arrive at their own version of those calls appears to be a developmental process, not a fixed inheritance.
A New Framework for Studying Animal Vocal Development
By focusing on how communication changes across an individual’s early life rather than comparing snapshots of adults from different groups, the study offers researchers studying other species a template for investigating how vocal systems emerge and diverge. “Understanding how communication develops during early life is fundamental to understanding animal behavior,” Giragosian said, adding that the findings fit into a broader body of research suggesting primate communication is more flexible and dynamic than previously recognized.
Giragosian and her colleagues argued that the ontogenetic approach, tracking how a trait unfolds over an individual’s development rather than comparing static adult populations, could prove useful well beyond chimpanzees. Many studies of animal communication compare fully grown individuals across groups and infer that any differences must be innate, since the animals were never observed as they acquired the trait in the first place. By instead following young chimpanzees as their calls changed month by month, the research team could show directly that population-specific patterns build up gradually, rather than assuming that conclusion from adult data alone. “By examining vocal development through an ontogenetic lens, the study provides a valuable framework for investigating how communication systems emerge and diversify within animal populations,” the authors wrote. The study was published online in the journal PLoS ONE, with the full dataset and methodology available in the peer-reviewed paper.
This article was produced with the assistance of AI and reviewed by Morning Overview editors prior to publication.
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