The part of the human brain that is linked to mankind’s unique sense of empathy also grows to the same scale in an array of other primates, according to a new study.
The findings, which came as a surprise to researchers, don’t suggest chimpanzees will be getting talk shows anytime soon. Instead the study shows that “the difference between us and great apes is incremental,” said lead researcher Amy Bauernfeind, a GW doctoral candidate. “That, in fact, we’re just seeing an expansion of an already present pattern that exists in primates.”slender loris.
Wedged between lobes on both sides of the brain’s main processing hub, the insula has been associated with functions that include recognition of oneself and emotions, empathy, and the processing of music and language—the kinds of cognitive advances, the authors wrote, that may have helped distinguish mankind and its social interactions.
In particular, the group was interested in measuring the volume of the whole insula as well as each of its components. For all 30 species they examined the left insula; for humans and great apes, they looked at both left and right insulae.
What the researchers expected to find, Ms. Bauernfeind said, was that the volume of the whole insula would be uniquely large among humans—and it was, but only because humans have the largest brains of the group. (For example: Despite having roughly the same body size as chimpanzees, mankind’s closest living relatives, the human brain is three times as large the chimp’s, she said.)
Once the researchers adjusted for overall brain size, a pattern emerged across the primates: as the size of the brain increased, the insulae grew slightly more than the rest of the brain. The pattern was strong enough that it could be used to predict measurements.
Among the insula’s individual parts, the piece that grew the fastest was the one linked to empathy. And when researchers compared that piece of the insula in chimps to humans, they were surprised to find that in humans it notched a bigger increase than other regions linked to cognitive functions, including language, said Ms. Bauernfeind.
Despite the other primates’ accelerated growth in that section of the insula, Ms. Bauernfeind said the sheer volume of it in the human insula is “pretty astounding when you look at it compared to other primates.” For instance, that section is about seven times bigger than in a chimp and three times bigger than in a bonobo. And that counts for something: The bigger the brain, the more neurons and connections there are to process and relay signals, creating a more “fine-tuned” process, the authors wrote.
Empathy is high on the “long list of cognitive capacities that are uniquely human,” said Ms. Bauernfeind. So although a chimpanzee’s insula is bigger than a macaque’s, and a gorilla’s is bigger than a chimp’s, “ours is much larger than theirs,” said Ms. Bauernfeind, “and perhaps that gives us the ability to empathize.”
—By Danny Freedman