Researchers have documented a distinctive cultural habit among a group of chimpanzees in the Chimfunshi Nature Reserve in Zambia. The behavior involves the deliberate placement of blades of grass into the ear canal, and in some cases, into the anal opening. Observers suggest that this practice spreads through social learning; younger or less experienced individuals imitate their more experienced peers, reinforcing bonds within the troop and signaling group identity.
In 2010, a female chimpanzee named Julie began carrying a piece of grass in her ear as she moved about the forested enclosure. Over the next few years, the behavior expanded to eight of the twelve chimpanzees in that specific community. Importantly, the pattern did not appear in other groups nearby, indicating that this is a local cultural tradition rather than a species-wide habit. Even years later, two members of this group continue to maintain the grass-in-ear habit, underscoring the persistence of the custom within that social circle.
Another notable phase emerged in August 2023 when a male chimpanzee, Juma, first inserted a blade of grass into his ear. This initiated a gradual cascade: by the end of August, five additional chimpanzees in the same group, plus one migrant individual, had adopted the practice. Around the same time, Juma began introducing grass into his anal canal, and the behavior quickly spread to other members of the troop. Within days, several more individuals joined the pattern, suggesting a robust transmission of the behavior through social observation and imitation rather than through genetic inclination or random chance.
Scientists recognize these actions as a cultural tradition within the chimpanzee community. The repeatable demonstrations by certain individuals create a shared repertoire that others can observe, imitate, and integrate into their own behavioral toolkit. These findings align with broader observations of primate cultures, where actions learned from peers can become defining features of a group’s social fabric. The impulse to imitate may serve multiple social functions: it helps individuals feel connected to relatives and peers, reinforces intra-group cohesion, and signals belonging to a specific community with its own distinctive practices.
Further reflection on this topic considers the social dynamics that foster such traditions. When a behavior is useful, visible, or merely novel within a group, it becomes more likely to spread. Individuals who perform the behavior may gain social leverage, while those who adopt it can strengthen bonds with influential group members. Over time, the practice can reach a stable frequency within the troop, even if it remains absent in neighboring groups, highlighting the strength of localized cultural patterns in chimpanzees. These patterns provide a window into how culture evolves in non-human primates, offering a mirror to human social learning and the ways communities develop unique rituals through shared observation and practice.
In reviewing these observations, researchers emphasize that the grass-in-ear and grass-in-anus behaviors appear to be learned expressions rather than instinctual commands. The presence of multiple cases across different individuals within the same social group supports the interpretation of culture rather than mere coincidence. As with other animal cultures, the transfer of behavior is closely tied to social bonds, sibling ties, and the daily routines that keep a troop cohesive. The ongoing curiosity about such traditions continues to refine our understanding of how culture can emerge and persist in primate societies, reminding us that learning from peers is a powerful force across the animal kingdom.