For the first time ever, scientists have witnessed the acquisition and spread of a new behavior — two new feeding methods — among wild chimpanzees. It's an 'extraordinarily rare' observation that points to the origins of social learning in both chimps and humans.

Chimps are among the most cultural of all non-human primates. To date, no less than 39 behaviors have been observed among chimpanzees that are socially acquired, the vast majority of them in the domain of tool-use. Researchers have also translated the meaning of over 60 chimp gestures. But previous investigations into how behaviors are transmitted among individuals have only been carried out among captive populations. The remarkable new observations are the first to document cultural transmission in wild chimpanzees.

Ideas Worth Spreading

The researchers — scientists from the University of St Andrews, Anglia Ruskin University, the University of Neuchatel, and the Universite du Quebec — were fortunate to observe the spread of two variations of "leaf-sponging," which is a common behavior among chimps. Typically, the Sonso chimpanzee community living in Uganda's Budongo Forest manufacture leaf-sponges by folding and chewing leaves in their mouth. They then dip them in a water source to drink.

But during six days of observations, the researchers watched as various individuals acquired two completely new behaviors: leaf-sponge re-use — where they use a sponge that had been left from a previous visit — and moss-sponging — where they produce a sponge made of moss or a mixture of leaves and moss. Neither of these behaviors had ever been seen before in the Sonso chimps.

It all started with the group's 29-year-old alpha male who made a moss sponge and began extracting water while being observed by a dominant adult female. Over the course of the next week, seven individuals adopted the practice. The researchers were able to confirm that six of these had observed the behavior before adopting it themselves (the seventh was seen to re-use a discarded moss sponge).

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In addition, the scientists documented a 12-year-old sub-adult male retrieve and use a discarded leaf sponge. Eight individuals adopted this technique in turn, but only four of them first observed another individual performing this behavior.

Social Networking

"Here, we present a novel, dynamic network-based diffusion analysis to describe the acquisition patterns of novel tool-use behavior in the Sonso chimpanzee community," note the authors in their study. "We find strong evidence for social transmission of [new behaviors] along the innovators' social network, demonstrating that wild chimpanzees learn novel tool-use behaviors from each other and supporting the more general claim that some of the observed behavioral diversity in wild chimpanzees should be interpreted as 'cultural.'"

A visualization of the static interaction networks for the moss-sponging behavior for all 30 individuals. (Hobaiter et al/PLoS)

That said, the study doesn't really explain the mechanisms behind social learning. The authors write:

Chimpanzees display a range of social learning mechanisms, including emulation and imitation, similarly to some monkey species. Teaching and imitation are often said to be central in the diffusion of human culture, but other social learning mechanisms can also generate behavioral traditions. For example, early hominins who contributed to the Oldowan technology (2.6 mya) may have relied on emulative processes rather than imitation, in contrast to the later Acheulean technology. However, as our results do not allow us to identify the precise learning mechanism employed during the social transmission of moss-sponging, it remains possible that this may vary from those on which humans rely to transmit their culture. Until the precise nature of these learning mechanisms is established, questions will remain about potential evolutionary discontinuity in the transmission of "cultural" behavior.

Nevertheless, although social learning mechanisms are important, our data support a growing literature that refutes a strong distinction between individual and social learning. Both rely on the same basic understanding of physical cognition and only differ in the presence or absence of a task-related social memory.

This study may not be a scientific bombshell, but it does indicate that group-specific behaviors in wild chimps can be socially learned. This is exciting because it's empirical evidence showing that the attribute, or prerequisite, for culture originated in a common ancestor of great apes and humans. In fact, long before the emergence of modern humans.

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Read the entire study at PLoS Biology: "Social Network Analysis Shows Direct Evidence for Social Transmission of Tool Use in Wild Chimpanzees".

Images: C. Hobaiter