Bonobos Show Optimism Through Laughter, Revealing Emotional Links to Humans

In a groundbreaking study, researchers from Indiana University have demonstrated that laughter can significantly enhance the mood of bonobos, our closest living relatives, thereby illuminating potential evolutionary links between human and primate emotions. The research, published in the journal *Nature Scientific Reports* on June 30, 2025, reveals that bonobos exposed to the sound of laughter exhibit increased optimism, suggesting that such emotional responses may date back millions of years to a common ancestor shared by humans and bonobos.

The study involved a series of cognitive-bias tests designed to assess the emotional states of bonobos when exposed to laughter. Lead researcher Sasha Winkler, a primatologist at Duke University, stated, "We know that other apes, like chimpanzees, have contagious laughter during play. We were wondering if that behavior could be explained by positive emotions produced from the sound itself." During the experiment, bonobos were trained to identify two types of boxes: one that consistently contained a treat and another that was always empty. The introduction of a third ambiguous box was paired with either recorded laughter or neutral sounds. The results indicated that bonobos were more likely to approach the ambiguous box when they heard laughter, suggesting a shift in their mood toward optimism.

Erica Cartmill, the senior author and director of Indiana University’s Cognitive Science Program, remarked, "The tendency to behave more optimistically after hearing laughter suggests that the sound alone induced a positive emotional state in bonobos." This finding marks the first experimental evidence that laughter in great apes can influence both mood and cognitive expectations similarly to humans. Prior studies have drawn parallels between human laughter and play calls emitted by great apes, suggesting a shared evolutionary lineage.

The phenomenon of emotional contagion—where one individual's emotions can induce similar feelings in others—is fundamental to understanding empathy, as emphasized by Winkler. She noted, "Studies like ours can help to untangle the evolutionary building blocks of empathy, communication, and cooperation in humans." This advancement in understanding emotional dynamics among primates emphasizes the significance of social sounds, such as laughter, in fostering positive emotional states.

The research team included notable figures and experts, including Dr. Amy K. Kline, a psychologist specializing in primate behavior at the University of Southern California, who emphasized the broader implications of understanding positive emotions in animal behavior. “Exploring how positive affect influences cognition can lead to insights not only into primate behavior but also into human social interactions,” she stated.

As researchers aim to explore whether similar effects of laughter exist in other primate species, including chimpanzees, they will also investigate how variables such as social context—laughter from familiar versus unfamiliar individuals—affect emotional responses. The legacy of bonobo Kanzi, known for his remarkable communication skills, was also acknowledged, highlighting the need for continued research into the emotional complexities of these endangered species.

This study not only contributes valuable insights into the emotional lives of bonobos but also underscores the shared emotional heritage that may connect humans and their primate relatives. As the research progresses, it opens avenues for a deeper understanding of the evolutionary roots of empathy, communication, and social cohesion, suggesting that the simple act of laughter carries profound implications across species.

For now, the discovery that bonobo laughter brightens their expectations offers a glimpse into the emotional world of primates, further solidifying the notion that laughter—a seemingly simple act—has been an essential aspect of social bonding and emotional regulation for millions of years.