Did Bugs Give Ancestral Primates a Bigger Brain?

Clever capuchin monkeys locate lots of insects and other invertebrates to eat when seasonal ripe fruit supplies run low. Evolutionary anthropologists believe these monkeys are showing us how the ingenuity of humanity’s ancestors tapped into a nutritious fallback food source that enabled them to evolve bigger, better, more human brains.

Bugs—The New Brain Food

“Challenges associated with finding food have long been recognized as important in shaping evolution of the brain and cognition in primates, including humans,” explains Dr. Amanda Melin, lead author of the study just published in the Journal of Human Evolution. “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.”

Wild capuchin monkeys locate and extricate insect snacks year-round, but when their favorite fruits are out of season, they really put their brains and hands to work filling in the menu with delectable bugs. (Of course, we all know that true bugs are insects with piercing, sucking mouthparts. The study focused on insects in general as well as any other invertebrates the capuchins cared to consume, but in the media the lot are loosely referred to as “bugs,” so we follow the same convention in this news story.) “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 says. “These results suggest embedded insects are an important fallback food.”

What They Saw

In order to demonstrate the ingenuity of these monkeys at “seasonal extractive foraging,” Melin’s group logged 436 hours of wild-monkey–watching in ten-minute chunks over a six-year period in a Costa Rican seasonally variable tropical forest. They logged each time a capuchin located, extricated or plucked, and consumed an invertebrate. They kept track of which ones they ate (caterpillars, grubs, ants, wasps, termites, katydids, stink bugs, cicadas, moths, snails, etc.), how long it took them to dig them out of their hiding places (crevices, curled up leaves, tree holes, hives, dirt, etc.) and how long it took them to gather them or to get at the good parts by evisceration, ripping off the exoskeleton and wings, or extraction from protective shells. Altogether they recorded 6,223 times a monkey ate an invertebrate and how long it took him to do it.1

The team also kept up with fruit picking, which they noted was considerably easier. They left out all the episodes of “extractive frugivory” in which the monkeys had to pound the fruit to get the parts they wanted because they might get to eat a hidden bug as a bonus. While the monkeys would thus kill two birds with one stone, so to speak, such activities would complicate the statistical analysis.1 Correlating their findings with seasonal patterns, the team concluded that “Capuchin frugivory [fruit eating] was significantly seasonal and closely matched variation in fruit abundance. . . . Capuchin faunivory [“bug” eating] was also significantly seasonal.”1

Finding Food and Becoming Human

Now what does being smart enough to meet the challenge of seasonal variations in food supply by finding the food needed to fill in the gaps have to do with becoming human? Well, primate animals—including those alleged to be ancestral hominids—have smaller brains than humans. Evolutionists look for ways to explain how humanity’s ancestors got bigger brains and how they got smarter. Melin explains, “Capuchin monkeys are excellent models for examining evolution of brain size and intelligence. For their small body size, they have impressively large brains. 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.”

Not all capuchins are equally evolved, Melin indicates. The gracile, untufted Cebus genus tropical rainforest-dwelling capuchin monkeys (the kind in this study) cleverly beat snails or fruits against tree branches to get at the goodies inside. Far more clever and even better at using tools however are the robust tufted Sapujus genus capuchin monkeys native to drier temperate regions of Africa where they have to cope with much more significant seasonal changes. Though this study did not include such monkeys, Melin says, “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. This may explain the occurrence of tool use in some capuchin lineages, but not in others.” Believing the two varieties of capuchins diverged millions of years ago, Melin says, “We predict that the last common ancestor of Cebus and Sapajus had a level of SMI [sensorimotor intelligence] more closely resembling extant Cebus monkeys, and that further expansion of SMI evolved in the robust lineage to facilitate increased access to varied embedded fallback foods, necessitated by more intense periods of fruit shortage.”

Parallel Evolution in Monkeys and Man

How does Melin’s team make the leap from monkeys to man? No one claims that capuchin monkeys are in the human lineage. Rather, the authors contend that the evolution of their brains, skills, and cognitive abilities is an example of parallel evolution2 and that we can therefore learn more about human brain evolution by studying clever capuchins.

After all, insects are still on the human menu in some parts of the world, and consumption varies according to the availability of other foods. Isotope analysis of the extinct gorilla-like “hominin” Paranthropus robustus suggests it had a seasonally varied diet that included termites and underground tubers, both of which would have required some effort to dig up. Chimpanzees eat termites that they extract with great effort too, and of course evolutionists view chimps as our closest living cousins. Foraging for food—fruit or fauna—is aided by spatial memory and the ability to use of whatever natural “tools” are at hand. Shifting gears to search for alternate types of food offers its own challenges. The researchers therefore reason that perhaps meeting the challenge of seasonal changes in the menu by having to ingeniously search and extract insects propelled our ancestors up the evolutionary ladder by favoring increasingly complex brain development fueled by nutritious foods year-round.

Eating Our Way up the Evolutionary Ladder

While good nutrition and mental stimulation during a humans child’s developmental years promotes optimal brain development, all that development is human—neither higher nor lower on the evolutionary scale than his or her human parents. So, do animals that are most successful and ingenious at locating alternative food sources in a pinch evolve brains of newer, more complex kinds of creatures? Nothing in biological observations has ever demonstrated such an occurrence, and certainly nothing in this study showed such a thing. All the subjects in this study were monkeys. The researchers suggested comparison of these capuchin monkeys to other varieties of capuchin monkeys. Some varieties are more ingenious than others, but they are all monkeys of the same kind, and no evolution is in evidence.

There is no known mechanism by which an ape-like animal can evolve a new and more complex brain.

In their efforts to explain how primate ancestral animals could gradually evolve both bigger brains and greater intelligence and thereby presumably become human, evolutionists discuss many “possibilities.” A typical suggestion is that learning to walk on two legs allowed the hands to be free to make tools and the eyes to take in the vast wonders of the world, stimulating the brain to think big thoughts and grow bigger in the process. The brighter among the ancestral bunch learned to process and cook their foods and by thus consuming calories more efficiently they could spend less time foraging and more time exploring their world, again stimulating their well-nourished brains to grow bigger. Add in some cooperation and social interaction around the campfire and you have the makings of the typical current evolutionary view of human history.

So what’s the problem? From a scientific perspective, there is no evidence in biology that creatures evolve into increasingly complex new kinds of creatures. There is no known mechanism by which an ape-like animal can evolve a new and more complex brain. Nutritious food and mental stimulation can help you make the most of the brain you have, but unlike Scarecrow in the Wizard of Oz, you are stuck with the kind of brain your DNA directs you to have, be it human or animal.

You can read more about culinary theories in evolutionary anthropology at

Of Monkeys and Man

Suffice to say, God created Adam and Eve in His own image on the same day He created the land animals, about 6,000 years ago. Humans did not evolve from animal ancestors. While we humans often fail to use all the intelligence God gave us, we still possess brains with abilities that far surpass those of any animal, and we have those because God created them that way. He also endowed us with a spiritual nature without any parallel among animals and the promise of an existence that will not end with our deaths. We are able, unlike animals, to comprehend and have fellowship with our Creator. We also are accountable to accept the offer of His grace through Jesus Christ to atone for our sins and rebellious nature. Capuchin monkeys are clever critters, but they do not explain what we humans need to know about our origins, our intelligence, our nature, or our eternal destiny.