Number of neurons makes human brain powerful, not structure

New research suggests the human brain isn't special. It's just a bigger, better primate brain.

"People need to drop the idea that the human brain is exceptional," Vanderbilt University neuroscientist Suzana Herculano-Houzel said in a news release.

Herculano-Houzel recently led a team of researchers in the search for the physiological source of human intelligence.

Previous studies have posited that the expansion of the human prefrontal cortex -- the control room for abstract thinking, complex planning and decision making -- explains humans' advanced neurological abilities.

When Herculano-Houzel and her colleagues compared human brains to the brains of other primates, they found comparable prefrontal cortex volumes.

Just like the brains of macaques, baboons, marmosets, galagos, owl monkeys and capuchins, the human brain devotes 8 percent of its neurons to the prefrontal cortex. The ratios of gray and white matter are also similar.

Human brains, being bigger, simply have far more neurons, the new research shows.

"Our brain is basically a primate brain," Herculano-Houzel said. "Because it is the largest primate brain, it does have one distinctive feature: It has the highest number of cortical neurons of any primate. Humans have 16 billion compared with 9 billion in gorillas and orangutans and six-to-seven billion in chimpanzees. It is remarkable, but it is not exceptional."

Herculano-Houzel says it was the development of cooking and the accompanying boost of calories that allowed humans to develop a much bigger brain.

Prepared foods were made possible by the first stone tools. By slicing, dicing and mashing, early humans got more calories without using as much energy.

"Those early tool makers had brains about the same size as gorillas," said Herculano-Houzel. "But, beginning about 1.8 million years ago, the brains of our ancestors began growing steadily, tripling in size over the next 1.5 million years."

The latest research on the evolution of the human brain was published in the journal PNAS.