DURHAM, N.C. -- In a study of orangutans living on the Indonesian islands of Borneo and Sumatra, scientists from Duke University and the University of Zurich have found what they say is the first demonstration in primates of an evolutionary connection between available food supplies and brain size.
Based on their comparative study, the scientists say orangutans confined to part of Borneo where food supplies are frequently depleted may have evolved through the process of natural selection comparatively smaller brains than orangs inhabiting the more bounteous Sumatra.
The findings "suggest that temporary, unavoidable food scarcity may select for a decrease in brain size, perhaps accompanied by only small or subtle decreases in body size," said Andrea Taylor and Carel van Schaik in a report now online in the Journal of Human Evolution.
Taylor is an assistant professor at Duke's departments of Biological Anthropology and Anatomy and of Community and Family Medicine. Van Schaik directs the University of Zurich's Anthropological Institute & Museum, and he also is an adjunct professor of biological anthropology and anatomy at Duke, where he had worked for 15 years.
"To our knowledge, this is the first such study to demonstrate a relationship between relative brain size and resource quality at this microevolutionary level in primates," they said.
Such a change would provide support for what Taylor called the "expensive tissue" hypothesis. "Compared to other tissues, brain tissue is metabolically expensive to grow and maintain," she said. "If there has to be a trade-off, brain tissue may have to give."
"The study suggests that animals facing periods of uncontrollable food scarcity may deal with that by reducing their energy requirement for one of the most expensive organs in their bodies: the brain," van Schaik added.