Orangutans’ turn to cultural knowledge to learn the foods of the forest.

By Dr Elliot Howard-Spink

Adult orangutans eat hundreds of different types of food in the wild, but how do they learn what to eat? In our recently published study, we investigated whether immature orangutans must learn knowledge from other individuals to develop their exceptionally broad diets. We analysed over a decade of data previously collected on wild Sumatran orangutans in the Suaq Balimbing Research Area to characterize how immature orangutans engage in behaviours hypothesised to be important for diet learning. This included:

1. How frequently immatures associated with other individuals.

2. Whether orangutans would be in close proximity when associated with other individuals (which can lead to higher rates of exploration, and a higher likelihood that immatures explore similar objects and places to other individuals; we call these effects ‘enhancement’).

3. When in close proximity, whether orangutans would observe of other individuals who are feeding (‘peering’), which can further enhance their likelihood of exploring new foods.

4. How the effects of these ‘social states’ on immature orangutans’ exploration changes over the course of their development, as we all as the number of times immatures would explore each type of food item before they successfully learnt to identify and eat it.

However, we could not identify how these social influences shape long-term diet development through analysing existing data alone. We only had snapshots of data describing the different behaviours of orangutans in the wild, and this prevented us from knowing exactly how broad an individual’s diet was at any one time.

We therefore combined the results from these analyses into a carefully designed simulation model, and simulated wild orangutans’ experiences throughout immaturity (ages between 0-15 years) to see if and how these social experiences shape orangutans’ long-term diet development.

We found that when simulated orangutans could engage in all behaviours that they perform in the wild (including peering & enhancement), they developed adult-like diets at ages that were statistically indistinguishable from wild individuals. This result confirmed that our simulation was able to capture the dynamics of real-world processes exclusively through calibrating it with data from wild individuals. We then proceeded to ‘switch off’ different forms of social learning from our simulation to assess their effects on diet development.

Even though simulated immatures were presented with almost 148,000 opportunities to encounter and explore food items across immaturity, they did not develop adult-like diets if they could not peer at other individuals, as peering led to an important upregulation of immatures’ exploration when exposed to food. Similarly, when we also removed ‘enhancement’ from the simulation, diet development was drastically slower and never came close to reaching adult levels (even though immatures were still provided with the same massive number of opportunities to explore different foods).

Our results indicate that orangutans’ diets are ‘culturally dependent repertoires’: sets of knowledge that are broader than any individual could produce through their own exploration. Our results reaffirm the need for rehabilitation and reintroduction programs to continue to teach orangutans what to eat prior to release into the wild, thus ensuring that released individuals can successfully identify available food items. More broadly, our results indicate that humans are not unique in the construction of cultures that are broader than any lone individual could produce.

Our findings push back the evolutionary roots of ‘culturally-dependent repertoires’ to the ancestors of hominids (humans & great apes). In extension, our results provide further evidence that the cultures of hominins were likely broader than what is suggested by surviving artefacts alone, and included rich repertoires of knowledge used for daily decision making.

The paper is available to read at Nature Human Behaviour:

Howard-Spink, E. et al. Culture is critical in driving orangutan diet development past individual potentials. Nat. Hum. Behav. (2025). https://doi.org/10.1038/s41562-025-02350-y