Evolution: less food = smaller brain in orangutans
October 23, 2006
A new study has linked diet to evolutionary brain size in orangutans living on the Indonesian islands of Borneo and Sumatra.
The research, published in the Journal of Human Evolution by researchers from Duke University and the University of Zurich, found that orangutans inhabiting areas in Borneo where food supplies are frequently depleted may have evolved comparatively smaller brains than orangutans living in more fruitful parts of Sumatra.
"[Our] 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, an assistant professor at Duke's departments of Biological Anthropology and Anatomy and of Community and Family Medicine, and Carel van Schaik, director the University of Zurich's Anthropological Institute & Museum and an adjunct professor of biological anthropology and anatomy at Duke.
Young orangutan in Borneo. Photo by Rhett Butler
"Compared to other tissues, brain tissue is metabolically expensive to grow and maintain," Taylor 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," added van Schaik.
"This brings us closer to a good ecological theory of variation in brain size, and thus of the conditions steering cognitive evolution," van Schaik continued. "Such a theory is vital for understanding what happened during human evolution, where, relative to our ancestors, our lineage underwent a threefold expansion of brain size in a few million years."
The researchers noted that the biggest difference were found between orangutans living in Sumatra, which is less affected by El Niño disruptions than can reduce the availability of fruit, and northeastern Borneo, where "soils are poorer, access to fruit is most iffy and the impact of El Niño events can be significant."
"The eastern parts of Borneo suffer more from El Niño-related droughts than parts of western Borneo," the scientists wrote. "The effects of El Niño on tropical rain forest composition and diversity are also more marked in eastern compared to western parts... [producing] an environment for orangutans of eastern Borneo that is at times seriously resource-limited." During lean times, wrote the scientists, the apes have to "resort to fallback foods with reduced energy and protein content, such as vegetation and bark,"
Orangutans are closely related to humans, sharing about 97 percent of our genetic material. Still they are highly threatened by poaching and habitat loss in their native Borneo and Sumatra. A recent report from the Wildlife Conservation Society said that Indonesia's population of orangutans fell nearly 43 percent in the past decade, from 35,000 in 1996 to 20,000 today.
Saving Orangutans in Borneo. I'm in Tanjung Puting National Park in southern Kalimantan on the island of Borneo. At 400,000 hectares (988,000 acres) Tanjung Puting is the largest protected expanse of coastal tropical heath and peat swamp forest in southeast Asia. It's also one of the biggest remaining habitats for the critically endangered orangutan, the population of which has been great diminished in recent years due to habitat destruction and poaching. Orangutans have become the focus of a much wider effort to save Borneo's natural environment. We are headed to Campy Leakey, named for the renowned Kenyan paleontologist Louis Leakey. Here lies the center of the Orangutan Research Conservation Project. Established by Biruté Mary Galdikas, a preeminent primatologist and founder of the Orangutan Foundation International (OFI), the project seeks to support the conservation and understanding of the orangutan and its rain forest habitat while rehabilitating ex-captive individuals. The Orangutan Research Conservation Project is the public face of orangutan conservation in this part of Kalimantan, the Indonesia-controlled part of Borneo.
Orangutan population plunges 43% in Indonesia. The Wildlife Conservation Society-Indonesia Program (WCS-IP) said that Indonesia's population of orangutans fell nearly 43 percent in the past decade, from 35,000 in 1996 to 20,000 today. The decline has been caused by ongoing forest destruction and poaching in Kalimantan (Borneo) and Sumatra, the only two islands that still support wild orangutans.
This article is based on a news release from Duke University