Insect diet may have led to bigger human brains

Foraging for lean-season diet such as ants, slugs and bugs may have spurred the development of bigger brains and higher-level cognitive functions in early humans and other primates, a new study suggests.

"Challenges associated with finding food have long been recognised as important in shaping evolution of the brain and cognition in primates, including humans," said study lead author, Amanda D Melin from Washington University in St Louis.

"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," said Melin.

Based on a five-year study of capuchin monkeys in Costa Rica, the research provides support for an evolutionary theory that links the development of sensorimotor (SMI) skills, such as increased manual dexterity, tool use, and innovative problem solving, to the creative challenges of foraging for insects and other foods that are buried, embedded or otherwise hard to procure.

The study is the first to provide detailed evidence from the field on how seasonal changes in food supplies influence the foraging patterns of wild capuchin monkeys.

The study, co-authored by Hilary C Young, Krisztina N Mosdossy and Linda M Fedigan, all from the University of Calgary, Canada notes that many human populations also ate embedded insects on a seasonal basis and suggests that this practice played a key role in human evolution.

"We find that capuchin monkeys eat embedded insects year-round but intensify their feeding seasonally, during the time that their preferred food – ripe fruit – is less abundant," Melin said.

The study suggests that fallback foods can also play an important role in shaping brain evolution among primates that fall back on insect-based diets, and that this influence is most pronounced among primates that evolve in habitats with wide seasonal variations, such as the wet-dry cycles found in some South American forests.

"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," Melin said.

While it's hard to decipher the extent of seasonal dietary variations from the fossil record, stable isotope analyses indicate seasonal variation in diet for at least one South African hominin, Paranthropus robustus.

Other isotopic research suggests that early human diets may have included a range of extractable foods, such as termites, plant roots and tubers.

Modern humans frequently consume insects, which are seasonally important when other animal foods are limited.

This study suggests that the ingenuity required to survive on a diet of elusive insects has been a key factor in the development of uniquely human skills: It may well have been bugs that helped build our brains.

The study was published in the journal of Human Evolution.