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Monday, November 24, 2025

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Orangutans can’t master their complex diets without cultural knowledge

Researchers reveal just how much wild orangutans depend on social learning to build diets spanning hundreds of different foods.

Max Planck Institute of Animal Behavior

Orangutans Can’t Master Their Complex Diets Without Cultural Knowledge — image:
A young orangutan (Cinnamon) peers at her mother (Cissy) whilst using a stick to fish termites from a nest.
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Credit: Guilhem Duvot

When a wild orangutan leaves its mother after spending many years by her side, it has a mental catalog of almost 250 edible plants and animals, and the knowledge of how to acquire and process them.

A new study in Nature Human Behaviour reveals that no lone orangutan could build this encyclopedic knowledge through trial and error. Instead, this knowledge forms a “culturally-dependent repertoire”— a diverse set of knowledge that is only attainable through years of watching and exploring alongside others.

As humans, we must learn broad repertoires of knowledge to survive and thrive—ranging from local customs, to the skills to engineer new innovations like fishing spears and iPhones. Much of this cultural knowledge is too broad or complex for any single human to innovate from scratch in their lifetime. Rather, culture accumulates from the innovations of many individuals. Until now, it has been unclear whether similar processes are at play for wild non-human species. An international team of researchers has now investigated whether the breadth of wild orangutans’ diets exceeds what any one individual could acquire on their own within a relevant time frame.

“We provide convincing evidence that culture enables wild orangutans to construct repertoires of knowledge that are much broader than they could otherwise learn independently,” says first author Dr Elliot Howard- Spink, postdoctoral researcher from the Max Planck Institute of Animal Behavior, now a researcher at the University of Zürich.

“These diets must be the product of experiences and innovations of many other individuals, which have accumulated over time,” adds coauthor Dr Claudio Tennie, University of Tübingen. “The roots of humans’ cultural accumulation may therefore reach back at least 13 million years to our last common ancestor with great apes.”

Simulating how orangutans learn what to eat

The team wanted to know if young orangutans can independently learn their full set of edible plant and animal species before they become self-sufficient adults at around 15 years old—or if they need to learn this information from others. The researchers used extensive data collected on wild Sumatran orangutans living in the swamp forests of Suaq Balimbing, Indonesia. This included 12 years of daily observations, where the behaviors of orangutans were recorded every few minutes.

But this data set alone was not enough. The team needed to create scenarios in which young orangutans were cut off from different types of social interactions as they grew. “We would never do this to wild orangutans,” says Howard-Spink. Also, it was impossible for the scientists to follow orangutans every single day over the many years it takes the animals to grow up, while also recording all their learning opportunities. So, the scientists devised another way.

Using daily snapshots of real-life data, Howard-Spink built a simulation model that reenacted orangutans’ lives from birth to maturity at fifteen years old. The model incorporated three key social behaviors predicted to influence how the diet of orangutans develop: close-range observation of others while they ate foods in the forest (a behavior called ‘peering’); being in very close proximity to other orangutans who were feeding (which made them more likely to explore similar foods); or, simply being guided to suitable feeding sites, without any further social contact.

“Every single parameter of this model is based on our long-term data from wild orangutans,” says Dr Caroline Schuppli, who lead the study and is a group leader at MPI-AB. “It allows us to pinpoint which types of social interactions help young orangutans learn what to eat, and even to rank their importance.”

When all three types of social learning were available (the condition most similar to wild individuals), simulated orangutans cultivated adult-like diets—about 224 food types—at around the same age as wild orangutans. These similarities between the model and the wild confirmed the simulation’s accuracy and real-world applicability, the authors say.

“The fact that our simulation matched wild individuals’ development so closely is due to the extensive and uniquely detailed data collected from the wild at Suaq, and the hard work of a large team involved,” says Howard-Spink.

Discovering orangutans’ “cultural cuisine”

Howard-Spink then began cutting the simulated orangutans off from different social interactions. Just cutting off close-range observations (peering), had an effect: simulated orangutans had slower diet development and reached only 85% of the full wild diet repertoire by adulthood. But removing both peering and close-proximity associations left simulated apes with drastically narrower diets. These diets never approached the breadths possessed by wild adults, and essentially stopped developing well before the end of immaturity.

“Socially-isolated, simulated orangutans still had hundreds of thousands of opportunities to encounter food items during development,” says Howard-Spink. “But even massive amounts of exposure to food could not replace what was lost when they couldn’t engage in these social interactions.”

Says coauthor Andrew Whiten, University of St Andrews: “We’re seeing the strongest evidence yet that orangutan diets are culturally accumulated over many generations.”

The next step is to understand how this culturally-accumulated knowledge influences orangutans’ energy intake, survival, and success. “Given how much diet development suffers without social inputs, the effect of culture on orangutans’ daily lives is potentially profound,” adds Whiten.

The team will address this question as part of a further study. “We will again use empirically-validated simulations to understand how reliant orangutans are on cultural knowledge to survive and thrive in wild habitats,” says Schuppli.

Conserving accumulated cultures

Adult orangutans are generally solitary, making their long childhoods a precious window for cultural transmission. “In the wild, the constant presence of a mother, and fleeting associations with other individuals, are critical for orangutan learning and development during the early years,” says Schuppli. “It offers a crucial apprenticeship that paves the path to independence.”

With orangutan populations dwindling, this study has practical urgency. Orphaned apes, reintroduced without the full breadth of a wild diet, or introduced in different environments, may face starvation or poisoning from unfamiliar plants. “Reintroduction programs already teach orangutans to feed themselves outside captivity,” adds Schuppli. “Our study emphasizes how important this is to pass on their full cultural menu, so that these animals have the greatest chance of success in the wild.”

Journal

Nature Human Behaviour

DOI

10.1038/s41562-025-02350-y

Method of Research

Computational simulation/modeling

Subject of Research

Animals

Article Title

Culture is critical in driving orangutan diet development past individual potentials

Article Publication Date

24-Nov-2025

Wednesday, August 27, 2025

Be it feast or famine, orangutans adapt with flexible diets

Rutgers-led researchers find survival strategies of the great apes offer lessons for human health and diet management

Rutgers University

Bornean Orangutan — image:
Orangutans living in the wild adapt to different foods, depending on availability, maintaining an overall healthy balance.
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Credit: Ilya Raskin/Rutgers University

Humans could learn a thing or two from orangutans when it comes to maintaining a balanced, protein-filled diet.

Great apes native to the rainforests of Indonesia and Malaysia, orangutans are marvels of adaptation to the vagaries of food supply in the wild, according to an international team of researchers led by a Rutgers University-New Brunswick scientist. The critically endangered primates outshine modern humans in avoiding obesity through their balanced choices of food and exercise, the scientists found.

The researchers reported their findings, based on 15 years of firsthand observations of wild orangutans in the jungles of Borneo, in Science Advances.

“These findings show how wild Bornean orangutans adapt to changes in their environment by adjusting their nutrient intake, behavior and energy use,” said Erin Vogel, the Henry Rutgers Term Chair Professor in the Department of Anthropology in the School of Arts and Sciences, who led the study. “The work highlights the importance of understanding natural dietary patterns and their impact on health, both for orangutans and humans.”

Orangutans are one of the closest living relatives to humans, sharing a common ancestor, Vogel said. This evolutionary relationship means that orangutans and humans have similar physiological and metabolic processes, dietary needs and behavioral adaptations. Studying orangutans can provide insights into the evolutionary adaptations that might also be relevant to humans, she said.

Humans also exhibit metabolic flexibility, Vogel said, but modern diets high in processed foods can disrupt this balance, leading to metabolic disorders such as diabetes.

While orangutans reduce physical activity during low fruit periods to conserve energy, Vogel said, humans, especially those with sedentary lifestyles, may not adjust their energy expenditure to match their caloric intake, leading to weight gain and associated health issues.

“Understanding these adaptations can help us learn more about how humans can manage their diets and health,” Vogel said. “It also highlights the importance of conserving orangutan habitats to ensure their survival.”

The research was conducted at the Tuanan Orangutan Research Station in the Mawas Conservation Area in Central Kalimantan, Indonesia, on the island of Borneo. The conservation area, a peat swamp forest, protects about 764,000 acres, an area roughly the size of Rhode Island. Peat forests are richly biodiverse, ancient ecosystems with landscapes dominated by waterlogged trees that grow on layers of dead leaves and plant material.

Understanding the dietary strategies of orangutans can inform better nutritional practices for humans, said Vogel, who also is director of the Center for Human Evolutionary Studies at Rutgers.

“In essence, the research on orangutans underscores the importance of dietary balance and metabolic flexibility, which are crucial for maintaining health in both orangutans and humans,” Vogel said. “It suggests that modern dietary habits, characterized by high consumption of processed foods rich in sugars and fats, can lead to metabolic imbalances and health issues.”

In earlier studies, Vogel and an international team of colleagues established the patterns by which orangutans fed. Orangutans prefer to eat fruit because it is rich in carbohydrates, but when fruit is scarce, they switch to eating more leaves, bark and other foods that can provide more protein but fewer sugary carbohydrates. In times of high fruit availability, orangutans still consume protein but get most of their energy from carbohydrates and fats in the fruit.

“We wanted to find out how their bodies handle these changes,” Vogel said. “We tested how the availability of fruit affects their diet and how their bodies adapt to avoid energy imbalance. We looked at how they switch between different types of fuel – like fats and proteins – when preferred food availability changes.”

To conduct the study, Vogel, research colleagues, students and a staff that mostly included field technicians indigenous to the island of Borneo collected data for more than a decade on what the orangutans ate daily and analyzed their urine to see how their bodies responded to any nutritional changes. This required staying in close proximity to the ape in the equatorial, humid jungle from dawn until night.

The scientists made a number of key findings:

Orangutans avoid obesity as part of a response to the significant fluctuations – in both magnitude and duration – in fruit availability in their natural habitat. Unlike humans in Western culture, who have constant access to high-calorie foods, orangutans experience periods of both abundance and scarcity. The periods of scarcity and resulting low caloric intake, similar to humans’ intermittent fasting, may help maintain their health by reducing oxidative stress.
During periods of fruit scarcity, orangutans exhibit metabolic flexibility, switching to using stored body fat and muscle protein for energy. This allows them to survive when food is scarce.
During periods of fruit scarcity, orangutans exhibit behavioral adaptability, relying on reduced physical activity as well as stored energy and muscles to conserve energy. They rest more, go to sleep earlier, travel less and spend less time with other orangutans. This flexibility enables them to use body fat and protein for fuel when needed. They rebuild fat reserves and muscle when fruit availability is high.
The orangutan diet also prioritizes a consistent level of protein, which contrasts with a modern Western diet, which often can be rich in low-cost, energy-dense, protein-poor foods. Those choices contribute to obesity and metabolic diseases in humans.

This research builds on a report published earlier this year in The American Journal of Biological Anthropology, led by doctoral student Will Aguado, as the first author. This study found that orangutans at Tuanan get most of their protein from the leaves and seeds of just one out of nearly 200 species in the diet -- a vine called Bowringia callicarpa. The protein in this plant fuels orangutans through seasons of fruit scarcity and likely allows orangutans at Tuanan to persist and for their population to grow.

Other scientists on the study from Rutgers included Malcolm Watford, a professor in the Department of Nutritional Sciences, Rutgers School of Environmental and Biological Sciences; and former Rutgers doctoral student Rebecca Brittain, Tatang Mitra-Setia and Sri Suci Utami from Universitas Nasional in Indonesia, graduate students William Aguado, Astri Zulfa and Alysse Moldawer, all with the Department of Anthropology in the School of Arts and Sciences. Former graduate student Timothy Bransford, who also contributed to the study, is now at Eckerd College, St. Petersburg, Fla.

Researchers from the following institutions also contributed to the study: The Max Planck Institute of Animal Behavior and the University of Konstanz in Germany; Yale University; Jagiellonian University in Krakow, Poland; the University of Cincinnati; the University of Colorado; Eckerd College in St. Petersburg, Fla.; Universitas Nasional in Jakarta, Indonesia; National Research and Innovation Agency in Cibinong-Bogor, Indonesia; University of Zurich in Switzerland; Hunter College of the City University of New York; and the University of Sydney in Australia.

Explore more of the ways Rutgers research is shaping the future.

Orangutans native to the rainforests of Indonesia and Malaysia are being studied for their positive dietary habits by a Rutgers-led team of scientists.

Credit

Ilya Raskin/Rutgers University

Orangutan feeding [VIDEO]