Envisioning Brain Growth

A new study suggests that the parts of the brain that process visual information have fueled brain size

Skulls
Skull of Simonsius grangeri, one of the fossils used in the study. (Photo courtesy of Matt Borths and Duke Lemur Center; illustration by Jess Abel/Trinity Communications)

This is a summary of a story by Fedor Kossakovski on Trinity College of Arts & Sciences.

A new Duke University study is reshaping scientists’ understanding of primate brain evolution. Published in Science and led by Richard F. Kay, professor emeritus of Evolutionary Anthropology at Trinity and the Nicholas School of the Environment, the study suggests that vision is the primary driver of brain size increases in primate evolution. It has long been thought that the frontal lobe was responsible for the explosive growth of some primates’ brains.

Because brains do not fossilize, researchers examined skulls from both living and extinct primates — many of which came from the Duke Lemur Center Museum of Natural History. Using high-resolution micro-CT scans, they created digital models of the inner braincase.

These models allowed scientists to compare brain structures across species and track evolutionary changes over millions of years.

The study did find that the frontal lobe grew larger as the brain grew larger. But, researchers found no evidence that the frontal lobe grew at a faster rate in different primate groups, which challenges earlier ideas based on fossil skulls. Instead, all primates showed the same general pattern of brain growth.

The most significant changes occurred in the occipital, parietal and temporal regions of the brain, which are involved in processing visual information. These areas expanded rapidly in tarsiers and anthropoids, a group that includes monkeys, apes and humans. The researchers also found that these evolutionary changes coincided with larger optic nerves, suggesting increased visual input to the brain.

Kay said the findings reveal a different story about brain evolution: “The enlarged brains … turn out to be tied to vision much more than to the frontal lobe, which simply kept pace with overall brain size,” said Kay. 

To read more about the research, visit Trinity College of Arts & Sciences.