Origins of Human Cumulative Culture – UCL (2017)

Captain James Cook was fascinated by Polynesians’ ability to converse with each other. In Tahiti a high priest named Tupaia got on board and accompanied him along their voyage to Hawaii. Despite the fact that the two islands were separated by more than 2500 miles Tupaia was able to converse perfectly with Hawaiians. In order to maintain a common language these seemingly isolated islands must have been connected by frequent trans-oceanic voyages.

Genetical and ecological theory dictates that connectivity is a key for maintenance of diversity. That is what University College London researchers, lead by Andrea Migliano are aiming to understand. How does the patterns in connectivity of human cultures lead to and shape cumulative culture? High clustering (family ties) and low degree of separation (remote connections) among human groups is a pattern for cultural transmission that has emerged from the study.

Researchers have used an RFID tag methodology to track interactions among members of a society in Mbendjele BaYaka Pygmies and Phillipines. This type of methodology has been applied to many curious settings including interactions in a hospital. An RFID-tag study has shown that nurses are the most vulnerable and transmissive group in disease outbreaks. Similarly, movements of members of a leafcutter ant colony have been tracked while being kept in an artificial nest.

How did hunter-gatherers accumulate a large repertoire of plant uses that enabled them to survive in tropical rainforests? To answer this question, Gül Deniz Salalı has conducted a field research on the Mbendjele BaYaka Pygmies in the tropical rainforests of northern Republic of Congo over 8 months with her colleagues from University College London. Their research showed that long-term pair bonds between men and women allowed otherwise distant families to combine information on medicinal uses of plants. Living in multi-family camps, on the other hand, enabled Pygmies to exchange and accumulate plant knowledge related to cooperative foraging and social beliefs. Marital ties and group living allowed Congo hunter-gatherers to accumulate a vast diversity of plant uses. The following video by Gül Deniz Salalı was recorded during a year long field study and shows joint processing of medicinal plant by spouses:

BaYaka Pygmy hunter-gatherers using medicinal plants from G. Deniz Salali.

BaYaka Pygmies have been living in the tropical forests of Central Africa by hunting and gathering for thousands of years. There is almost no access to modern medicine. People rely on wild plants and traditional healers when they become sick. Plants are used for many non-medicine purposes as well such as poison to stun fish or hunt monkeys. There are other poisonous plants which are used to detect and punish cheaters in the community!

Gül Deniz needed to find a way to measure knowledge sharing network in a systematic way. Employing a quantitative ethnobotanical approach she asked about the uses of same plants to as many people as possible to see similarities in plant uses and sharing of knowledge. Moreover, she also wanted to test whether people who were close kin or who lived in the same camp shared knowledge more. In the past a researcher would ask people from whom they had learnt about plants. Gül Deniz found this method less reliable, since as often people give answers that are considered appropriate by their society. It is also hard for people to recall where their knowledge came from. For instance, the majority of the BaYaka told her that they learnt about plants from their mothers. They never mentioned their spouses. She found that spouses in fact shared a lot of knowledge on how to use a plant. She asked over 200 Pygmies about use of 33 plant species. Based on this inquiry, she was able to untangle who shared plant knowledge with whom by analyzing the similarity in plant usage by pairwise comparison of more than 20,000 hunter-gatherers. She then looked at what made it more likely that a pair of people shared more knowledge.

It turned out that use of a particular medicinal plant was very similar to that of their spouses. What is more interesting was that not only spouses shared knowledge on medicinal plant uses, but also in-laws or even people who were linked by distant marital ties (for example you and your spouse’s cousin). She observed joint production of medicine by parents for their sick children many times in the field. Spouses and relatives exchange information on medicinal uses as they care for their children, while children learn about plants as they receive treatment. In the following recording, for instance, you can see Semoi and her husband, Tokidya, boiling the bark of guka (Alstonia boonei) to use as a treatment for their son’s stomach-ache. Strikingly, mothers who used diverse group of medicinal plants had children with higher body-mass index.

Unlike medicinal uses of plants, knowledge related to foraging or social rules were shared regardless of family ties. Instead, people who were residing at the same camp had more similar uses of plants for those group-wide activities. The BaYaka often forage for fish, wild yams and honey in groups formed of campmates. I once went for a fishing trip with a group of BaYaka where we used the fruits of Brenania brieyi to poison fish. Everyone in the camp participates in these trips, where women and children pound the poisonous fruits and mix it with ashes. Then, they make dams in the river and pour the fruit mixture into the dams and wait for fish to get numb.

Fishing trip with Pygmy hunter-gatherers from G. Deniz Salali.

The BaYaka also use plants to regulate social life. For instance, the juice from the boiled bark of Erythrophleum ivorense is believed to be selectively poisonous: they poison liars and leave truthful people well. Co-residence of multiple unrelated families in camps helps the BaYaka exchange this type of plant knowledge that potentially enhances group coordination.

Social learning is not exclusive to humans. Some African apes use medicinal plants for similar diseases to humans and may acquire plant knowledge through the observation of other individuals.

Female chimpanzees have been shown to be highly influential for transmitting cultural traits and maintaining cultural diversity. Females move in between communities. Males fail to do so since other males never tolerate new incoming potential rivals. Females bring novel cultural traits and increase the cultural diversity of the community. Parallel to the migration of females groups sharing a culture also have a distinct genetic make up. Female genes therefore can delineate borders of cultural regions. Mitochondria (power generating organelles in higher organisms) are transmitted from mothers to their offspring and have its own DNA. Analysis of chimpanzee mitochondrial DNA has shown just that.

However, medicinal plant uses in chimpanzees are not comparable to the vast diversity of plants used by human populations. Studies indicate that hunter-gatherers’ complex social structure created an environment for transmission and accumulation of plant knowledge.

Human Nature