More food helps orangutans learn better

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 (Image: Pixabay CC0)
(Image: Pixabay CC0)
The adage "necessity is the mother of invention" is often used to describe the origin from which our cultural development springs. After all, necessity in times of scarcity has forced humans to constantly invent new technologies that have driven the remarkable cumulative culture of our species. But an invention only becomes cultural when it is learned and spread by many people. In other words, the invention must be socially transmitted. But what forces drive social transmission? A long-term study of wild orangutans over 18 years suggests that the answer can be found in the ecological habitat and the corresponding food availability of an animal.

A team from two Max Planck Institutes and the University of Leipzig studied how male orangutans learn from others and found that individuals that grew up in habitats with abundant food had a higher propensity for social learning. This finding shows how an animal’s ecological habitat can affect its opportunities for social learning and thus the likelihood that a new behavior can become an innovation with cultural traits.

"We have shown that the ecological resource availability of habitats has knock-on effects on an individual’s social learning opportunities, but also on its propensity for social learning over the course of evolutionary time," says first author Julia Mörchen.

Unique insights into the social learning of orangutans

The team from the Max Planck Institutes for Evolutionary Anthropology (MPI-EVA) and Behavioral Biology (MPI-AB) and the University of Leipzig studied adult male orangutans from wild populations in Borneo and Sumatra. "Due to their lifestyle, adult males offer unique insights into the social learning of orangutans," says Mörchen, a doctoral student at Leipzig University.

As soon as the males reach sexual maturity, they leave the habitats where they grew up and spend the rest of their lives as nomads, wandering long distances through the rainforest. "This means that males are similar to tourists and therefore need to learn important behaviors from experienced native orangutans, such as which foods are safe to eat," says Mörchen. To learn the necessary new skills, male migrants observe the local orangutans in a behavior known as "peering".

The researchers studied orangutans in Borneo and Sumatra and collected data on cases where male migrants observed ("peered") the locals. In both populations, they found that males spent more time around others and looked at them more often when food was plentiful in the area. The authors say that this is an indication that the ecological resource availability of a habitat can modulate an animal’s social learning. "In good times, orangutans spend more time in close contact and so there are more opportunities for social learning," says Mörchen.

Higher propensity for social learning

The result deepened when the team compared male migrants from Sumatra and Borneo to see how different the peering rates were. Sumatran orangutans live in habitats with a high food supply, while Bornean populations live with a low and fluctuating food supply. Thus, it was not surprising that males from Sumatran populations spent more time "peering" than males from Bornean populations. However, the finding persisted even after the effects of differences in food availability between the two orangutan habitats were taken into account. "So it’s not just because Sumatran males have more food available and therefore spent more time peering," says Mörchen. "We found that Sumatran males have a higher overall propensity to peer than their Bornean relatives." However, the authors say that the study cannot decipher the mechanisms of how these differences in peering propensity came about. "It could be the result of developmental effects of Bornean and Sumatran orangutans growing up under different ecological conditions," says Mörchen. "Or it could be the result of genetic differences between the species that separated around 674,000 years ago, or a combination of both."

Lead author Caroline Schuppli from the MPI-AB explains: "Our study provides insight into how ecology can affect cultural transmission. We show that ecological food availability influences the opportunities for social learning and thus the likelihood that new behaviors become cultural."

Lead author Anja Widdig from the MPI-EVA and Leipzig University adds: "The discovery that ecological food availability affects social tolerance and peering in the least sociable ape species, which are most distantly related to humans, points to a deep evolutionary origin of how the propensity for social learning modulated by corresponding food availability has evolved within the hominid lineage."

Original title of the publication in iScience :
Orangutan males make increased use of social learning opportunities, when resource availability is high , doi: 10.1016/j.isci.2024.108940

Julia Mörchen

Max Planck Institute for Evolutionary Anthropology Leipzig / Institute of Biology, University of Leipzig

341 97-36872

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Anja Widdig

Max Planck Institute for Evolutionary Anthropology / Institute of Biology, University of Leipzig

341 97-36707

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Dr. Caroline Schuppli

Max Planck Institute of Behavioral Biology

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Expanding the menu: Immigrant orangutans learn a lot about food from their native conspecifics