The fall of chimp civilisation
Human impact has reduced cultural behaviours in some great ape communities by more than 80%. Jeff Glorfeld reports.
Chimpanzees, our closest living genetic relatives and critically endangered across most of their natural territory, are losing many of their traditions, behavioral and cultural traits through human interference.
A new study in the journal Science based on the observation of nearly 150 African chimpanzee populations found that in some communities behavioural diversity had declined more than 80%.
A 1999 article in the journal Nature, co-authored by renowned ethologist Jane Goodall, notes that some cultural anthropologists believe culture requires language, making it uniquely human.
But in the biological sciences, Goodall writes, a cultural behaviour is thought to be one that is transmitted repeatedly through social or observational learning to become a population-level characteristic.
“By this definition,” she explains, “cultural differences (often known as ‘traditions’ in ethology) are well established phenomena in the animal kingdom and are maintained through a variety of social transmission mechanisms.”
Chimpanzees (Pan troglodytes) have shown well-documented, exceptionally high levels of behavioural diversity, including communication and foraging, says Christophe Boesch, from the Max Planck Institute for Evolutionary Anthropology, in Leipzig, Germany, and author of a 2013 article Wild Cultures: A Comparison between Chimpanzee and Human Cultures, published in The Quarterly Review of Biology.
Chimpanzees are also proficient tool-users, Boesch says, and many of their behaviours are inferred to be socially learned and therefore cultural.
Boesch is one of a huge number of scientists from around the world who participated in the latest research into chimpanzee behaviour. Lead author is Hjalmar Kuehl, also from the Max Planck Institute.
Because of the rapid population decline of the animals, the researchers were eager to find the extent to which chimpanzees’ behavioural and cultural diversity are affected by habitat fragmentation and population loss resulting from human activities.
One of the core areas of investigation by the scientists involves the “disturbance hypothesis”, originally proposed in a 2002 paper in the International Journal of Primatology, by Carel P van Schaik, from the University of Zurich, Switzerland.
Kuehl and his colleagues explain that under the “disturbance hypothesis”, because of human actions, behavioural traditions in great apes may disappear, not only with the complete extinction of a population, but also when the population remains, owing to resource depletion or a breakdown in opportunities for social learning.
“Major elements of human impact include habitat loss, degradation and fragmentation, which reduce population size, gregariousness and long-distance dispersal, weakening behavioural transmission,” they write.
The researchers applied a range of non-invasive techniques to collect environmental, social, demographic and behavioural information on previously unstudied chimpanzee communities, or communities not fully habituated to human observers, at 46 locations.
They collected data over a minimum of one annual cycle, observing between 12 and 30 months at 37 locations, and from one to 10 months in nine locations, in a systematic grid design that ranged from nine to 143 square kilometres.
They compiled data on the presence and absence of 31 known chimpanzee behaviours from these 46 chimpanzee communities, and complemented the data set with additional information about these same behaviours on another 106 chimpanzee communities from the published literature.
In total, 144 unique chimpanzee communities comprised the full data set.
Supporting the “disturbance hypothesis”, the researchers found that chimpanzee communities located in areas with a high degree of human impact exhibited an 88% reduction of behaviours, compared to communities with the least human impact observed.
“We are currently witnessing a decline in great ape populations at a rate of 2.5% to 6% per year due to human impact,” the researchers write. “Our results suggest that chimpanzee populations are losing their characteristic sets of behavioural traits and that a number of not yet discovered behaviours may be lost without having ever been described.”
The authors call for a new approach to conservation that considers behavioural diversity in addition to population size and trends for wildlife management.
“We anticipate the necessity for a new concept, ‘chimpanzee cultural heritage sites’, with which the behavioural and cultural diversity of this species might be recognised and protected,” they conclude.