Humans May Have Evolved Their Big Brains by Eating and Hunting for Insects

Humans are smart, but how and why we first developed our big brains has long been a cause for speculation among scientists. Now, they have a new theory. Researchers believe that figuring out how to survive on a lean-season diet of insects may have spurred the development of our bigger brains and higher-level cognitive functions.

"Challenges associated with finding food have long been recognized as important in shaping evolution of the brain and cognition in primates, including humans," said Amanda Melin, lead author of the new study, in a news release. "Our work suggests that digging for insects when food was scarce may have contributed to hominid cognitive evolution and set the stage for advanced tool use."

Previous research has shown that fallback foods help shape the evolution of primate body forms. For example, primates whose fallback diets rely on vegetation developed strong jaws, thick teeth and specialized digestive systems. This means that fallback foods might have influenced humans-more specifically, insects. In order to see how insect-eating might influence primate development, the researchers examined capuchin monkeys, which eat embedded insects year-round but intensify feeding seasonally.

"Capuchin monkeys are excellent models for examining evolution of brain size and intelligence for their small body size, they have impressively large brains," said Melin. "Accessing hidden and well-protected insects living in tree branches and under bark is a cognitively demanding task, but provides a high-quality reward: fat and protein, which is needed to fuel big brains."

Yet not all capuchin monkeys are created equal. The robust (genus Sapajus) and gracile (genus Cebus) capuchin lineages have differences in their tool use. The Cebus monkeys use clever food-foraging, such as banging snails against branches. But they don't measure up to their Sapajus cousins when it comes to innovative tool use. This is possibly because Cebus capuchins have occupied tropical rainforests while Sapajus monkeys spread into drier, more temperate and seasonal habitat types.

"Primates who extract foods in the most seasonal environments are expected to experience the strongest selection in the 'sensorimotor intelligence' domain, which includes cognition related to object handling," said Melin. "This may explain the occurrence of tool use in some capuchin lineages, but not in others."

The findings reveal how it's possible that our big brains mainly evolved from our search for food. Insects, in particular, were likely an important part of our diet in the past, and could have been a key factor in the development of uniquely human skills.

The findings are published in the Journal of Human Evolution.