Diet Linked to Brain Size in Primates
orangutan.
Credit: morguefile.com

Brain tissue is expensive for a body to produce, so when times are tough, some primates go with a smaller noodle, a new study suggests.

Scientists compared orangutans living on the Indonesian islands of Borneo and Sumatra. The subspecies Pongo pygmaeus morio, living in northeastern part of Borneo where food supplies were limited, had a smaller brain. 

“I think we are the first people to have demonstrated this in primates,” said lead author Andrea Taylor of Duke University.

The finding suggests that this type of selection could result in smaller brain size in humans as well.

“A resource-limited environment might in fact influence brains to the point where they are unable to be grown and maintained to the same size as other groups,” Taylor told LiveScience.com. “And if that can happen in orangutans we can say that it provides support for that possibility in Homo floresiensis as well.“

The Homo floresiensis is a member of human lineage that is assumed to have lived on the island of Flores in Indonesia about 18,000 years ago. In 2004, researchers found skeletal remains of a female and others that stood only 40 inches tall with a skull the size of a modern chimpanzee. Some scientists, however, argue that the remains are of ancestors of modern human pygmies who live on the island today and that their small stature was a result of a developmental disorder.

Compared with other body organs, brain tissue is metabolically costly. Therefore any adaptive benefits from a larger brain must exceed the extra energy required to grow and maintain the larger brain tissue, Taylor and colleagues write in the current online issue of the Journal of Human Evolution.

"This brings us closer to a good ecological theory of variation in brain size, and thus of the conditions steering cognitive evolution," said study co-author Carel van Schaik from the University of Zurich's Anthropological Institute & Museum. "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."