When you’re smiling, it may feel like the whole world is smiling with you, but a new study suggests that some facial expressions may not be so universal. In fact, several expressions commonly understood in the West—including one for fear—have very different meanings to one indigenous, isolated society in Papua New Guinea. The new findings call into question some widely held tenets of emotional theory, and they may undercut emerging technologies, like robots and artificial intelligence programs tasked with reading people’s emotions.

For more than a century, scientists have wondered whether all humans experience the same basic range of emotions—and if they do, whether they express them in the same way. In the 1870s, it was the central question Charles Darwin explored in The Expression of the Emotions in Man and Animals . By the 1960s, emeritus psychologist Paul Ekman, then at the University of California (UC) in San Francisco, had come up with an accepted methodology to explore this question. He showed pictures of Westerners with different facial expressions to people living in isolated cultures, including in Papua New Guinea, and then asked them what emotion was being conveyed. Ekman’s early experiments appeared conclusive. From anger to happiness to sadness to surprise, facial expressions seemed to be universally understood around the world, a biologically innate response to emotion.

That conclusion went virtually unchallenged for 50 years, and it still features prominently in many psychology and anthropology textbooks, says James Russell, a psychologist at Boston College and corresponding author of the recent study. But over the last few decades, scientists have begun questioning the methodologies and assumptions of the earlier studies.

Psychologist Carlos Crivelli was one of them. In 2011, he was working with his colleague, psychologist José-Miguel Fernández-Dols, at the Autonomous University of Madrid. Together, they came up with a plan to investigate Ekman’s initial research in Papua New Guinea. Crivelli and longtime friend and research partner, Sergio Jarillo, an anthropologist at the American Museum of Natural History in New York City, traveled to the Trobriand Islands off Papua New Guinea’s east coast, where about 60,000 indigenous Trobrianders live. These horticulturists and fishermen have been historically isolated from both mainland Papua New Guinea and the outside world. To learn all that they could, Crivelli and Jarillo embedded themselves in the local culture. They were adopted by host families and took clan names; Crivelli became “Kelakasi” and Jarillo, “Tonogwa.” They spent many months learning the local language, Kilivila.

When it came time to begin the study, they didn’t need translators or local guides. They simply showed 72 young people between the ages of 9 and 15 from different villages photos from an established set of faces used in psychological research. The researchers asked half the Trobrianders to link each of the faces to an emotion from a list: happiness, sadness, anger, fear, disgust, or hunger. The other half was given a different task.

Crivelli found that they matched smiling with happiness almost every time. Results for the other combinations were mixed, though. For example, the Trobrianders just couldn’t widely agree on which emotion a scowling face corresponded with. Some said this and some said that. It was the same with the nose-scrunching, pouting, and a neutral expression. There was one facial expression, though, that many of them did agree on: a wide-eyed, lips-parted gasping face (similar to above) that Western cultures almost universally associate with fear and submission. The Trobrianders said it looked “angry.”

Surprised, Crivelli showed a different set of Trobrianders the same faces, but he couched his questions in stories—e.g., “Which of these people would like to start a fight?”—to draw out more context. They, too, associated the gasp face with threatening behavior, Crivelli reports today in the Proceedings of the National Academy of Sciences . “The implications here are really big,” he says. “It strongly suggests that at least these facial behaviors are not pancultural, but are instead culturally specific.”

That’s not to say that emotions don’t elicit natural physiological reactions, Russell explains, but the study suggests that reactions and interpretations can vary from culture to culture. With the gasp face, for example, Russell speculates that the expression could be a natural response to urgent, distressing situations. Whereas Western culture has tied that expression to feeling fear, it might be that the Trobrianders associate the expression with instilling it. Crivelli agrees, and points to another culture whose ritualized dances feature a similar expression in a threatening fashion: the Māori of New Zealand.

Based on his research, Russell champions an idea he calls “minimal universality.” In it, the finite number of ways that facial muscles can move creates a basic template of expressions that are then filtered through culture to gain meaning. If this is indeed the case, such cultural diversity in facial expressions will prove challenging to emerging technologies that aspire to decode and react to human emotion, he says, such as emotion recognition software being designed to recognize when people are lying or plotting violence.

“This is novel work and an interesting challenge to a tenet of the so-called universality thesis,” wrote Disa Sauter, a psychologist at the University of Amsterdam, in an email. She adds that she’d like to see the research replicated with adult participants, as well as with experiments that ask people to produce a threatening or angry face, not just interpret photos of expressions. “It will be crucial to test whether this pattern of ‘fear’ expressions being associated with anger/threat is found in the production of facial expressions, since the universality thesis is primarily focused on production rather than perception.”

Social psychologist Alan Fridlund at UC in Santa Barbara, says the researchers’ level of immersion in the Trobrianders’ culture gives them a unique perspective on threat displays, and not relying on translators improves the study’s accuracy. “I think the real strength of this paper is that it knows its participants so well,” he says.

But he adds that the snapshot method may not be the best way to analyze how people view different facial expressions—after all, in everyday life, people see facial expressions in the context of what’s going on around them, he says. Another problem has to do with the study design—“happiness” was the only positive emotion that Trobrianders were given as an option, Fridlund says, which may have biased the results. For example, if the researchers had included “amusement” or “contentment” as answers, the apparent agreement over smiling might have disappeared.

Despite agreeing broadly with the study’s conclusions, Fridlund doubts it will sway hardliners convinced that emotions bubble forth from a common fount. Ekman’s school of thought, for example, arose in the post–World War II era when people were seeking ideas that reinforced our common humanity, Fridlund says. “I think it will not change people’s minds. People have very deep reasons for adhering to either universality or cultural diversity.”

*Correction, 18 October, 12:33 p.m.: This story has been updated to correct the number of Trobrianders and their way of life, and to better describe the questions asked of them.