Humans accumulate knowledge over generations, building vast bodies of expertise—a quality that scientists have long suggested helps make humanity unique. In order to explore how such “cumulative culture” arose, anthropologists examined the way in which hunter-gatherers known as the BaYaka Pygmies, living in the Republic of Congo, exchange information among large pools of people. Their findings, reported in the journal Current Biology on September 8, suggest that complex social structures of hunter-gatherers may have helped cumulative culture evolve.

The scientists focused on the way the BaYaka share their knowledge about tropical rainforest plants. “Knowing about plants is very important in forest hunter-gatherers, as they have very limited access to modern medicine,” says study lead author Gul Deniz Salali, an evolutionary anthropologist at University College London, who also notes that the BaYaka use plants as food and as poison in hunting and fishing. “I was interested in how hunter-gatherers accumulated so much knowledge on the forest and who shared what type of information with whom,” he says.

During eight months of fieldwork, the researchers catalogued uses of 33 different plants from 219 individuals from four camps. They found these uses fall into three main groups. Medicinal uses mostly focused on treating digestive and respiratory disorders. Foraging uses included the collecting of edible caterpillars. Social uses included plants thought to selectively poison dishonest fellow tribesmen.

Salali and her colleagues found that knowledge of medicinal plants was mostly shared among spouses, biological kin, and relatives through marriage, revealing the important role of family ties in passing information. “You learn about medicinal plants from your parents when you get sick as a child; when you grow up, you share that information with your spouse, who brings his specialized knowledge from his family,” Salali says. “Strong pair bonds and kin recognition allowed otherwise distant families to come together and exchange information.”

In contrast, plant knowledge associated with foraging and social uses was shared more widely among campmates regardless of relatedness, playing an important role in campwide activities that required cooperation. “When you live in groups and engage in group activities, types of knowledge that are relevant for those activities become public domain—for instance, using a particular fruit to poison fish or monkeys,” Salali says.

These findings suggest that knowledge sharing, and hence cumulative culture, depend on social networks. “More connections among people with different types of information mean more opportunities to combine and generate new types of information,” Salali says.

Salali says her next step is to compare plant knowledge and use in hunter-gatherers living in varying proximity to market towns in Congo. “I am interested in exploring the biological and cultural adaptations of groups in transition from a nomadic hunter gatherer lifestyle to a more sedentary farming way of life,” says Salali, whose work was part of the Hunter-Gatherer Resilience Project.

Anthropologist Michael Gurven at the University of California, Santa Barbara, who did not take part in this research, found the tracking of ethnobotanical knowledge interesting. But he sees problems linking these new findings with the emergence of cumulative culture—in particular, there were no direct measures of how information was spread from one person to another.

“The evolution of cumulative culture is a difficult phenomenon to study directly using observations in living people who all possess cumulative culture,” Gurven says. “Future work will need to better integrate mathematical models, experiments among humans and other social animals, and the kinds of ethnographic studies carried out by Salali and colleagues.”