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We Are What They Ate

We may have evolved large brains because of our ancestors' feeding behaviors

In 1758, Swedish biologist Carl Linnaeus dubbed our species Homo sapiens. We have proudly embraced that moniker—wise human—and we have the brains to prove it.

Today’s humans have brains that are three times larger than our Australopithecine ancestors and six times larger than should be the case for a mammal of the same overall size (González-Forero & Gardner, 2018). However, we do not yet know just what propelled the human brain to expand to its present size.

Seligman, Railton, Baumeister, and Sripada (2016) suggested that our large brain enables us to contemplate and plan for the future. That cognitive ability is so unique that they even proposed renaming our species Homo prospectus. These authors conceded that a few species of animals display some “unconscious” powers of prospection; however, they contended that these animals may not be capable of thinking more than a few seconds into the future. By contrast, our large brain permits us—both “consciously” and “unconsciously”—to peer far into the future. To be a human is thus to be a futurist.

Of course, engaging in future-oriented cognition ought to be of considerable adaptive value in a broad range of situations. In the game of survival, we can’t afford to be “one-hit wonders.” Nevertheless, it is entirely possible that prospective thought might have originated to serve a specific function. If so, then what might it have been?

One possibility is called the social brain hypothesis (reviewed by Dunbar, 2009). According to this popular hypothesis, more complex social networks require more elaborate neural computing systems in order to anticipate and respond to the behaviors of conspecifics, with some individuals being involved in long-term reproductive relationships. Still more remote kin relations also span long intervals of time.

Public domain
1590 painting by Giuseppe Arcimboldo depicts Rudolf II, Holy Roman Emperor from 1576, as Vertumnus, the ancient Roman god of seasons who presided over gardens and orchards.
Source: Public domain

Another possibility is that diet, not sociality, is the central driving force for increasing brain size. This ecological brain hypothesis stresses the many dietary challenges that must be confronted in the non-social environment: finding, growing, catching, storing, or processing food. Several different lines of evidence are providing mounting support for this hypothesis (reviewed by Rosati, 2017).

From the comparative perspective, Roberts (2012) examined both experimental laboratory investigations and field observations of animals’ food gathering, storing, and pilfering as well as studies of animals’ tool selection and use. The species that he considered included nonhuman primates, rats, black-capped chickadees, scrub-jays, and tayras. Roberts concluded that there is strong evidence for future-oriented cognition in animals. Indeed, the clearest demonstrations of anticipation and planning in animals come from species that cache and later retrieve food; these animals may need to be especially mindful of the future fate of their caches. Remarkably, some animals are able to place food in hundreds of safe places and retrieve it months later!

Another comparative study of both brain and behavior in 140 nonhuman primate species across all four primate groups—apes, monkeys, lemurs, and lorises—pursued these behavioral observations. DeCasien, Williams, and Higham (2017) recorded brain size, social complexity, and dietary complexity. They specifically grouped the foods the animals ate into: leaves alone, fruit alone, both leaves and fruit, and finally leaves, fruit, and animal protein. Their prime finding was that brain size was larger when fruit or protein was included in the primates’ diet; the animals’ social behavior proved to be less important.

Of course, cause and effect are difficult to determine with such correlational data. Perhaps consuming fruit or protein helps to grow a bigger brain. Other kinds of data and investigative approaches are needed to resolve this issue.

An innovative computational analysis has recently confirmed earlier ecological accounts. González-Forero and Gardner (2018) deployed an elaborate computer model to determine why our brains got so big. The model incorporated the energy needs of an adult human female to nourish her brain, body tissues, and reproductive activities. It further considered the balance between brain size and body size, recognizing that the brain is a glutton for energy: it constitutes merely 4 percent of our body weight, but it guzzles 20 percent of our energy intake.

Several different computer simulations were given a host of ecological challenges: for example, finding food in foul weather, preserving food to prevent spoilage, and storing food during famine or water during drought. Social challenges too were given to see how cooperation and competition affected brain and body weight.

The results suggested that ecological pressures were most likely to increase the size of our brain. The impact of cooperation and competition between individuals and groups proved to be much less important. In fact, cooperation actually produced decreases in brain size, perhaps because this factor reduces the burdens placed on any one individual’s brain.

As a final note, I would observe that comparing brain size and behavioral proxies of “intelligence” across species has long proven to be a difficult and controversial undertaking. Variations in overall brain size or even in the size of particular brain structures may not strongly correlate with specific cognitive processes (Logan et al., 2018). That said, there seems to be little doubt that our cognitive systems have been shaped by the food seeking, storing, preserving, and preparing behaviors of our evolutionary ancestors. Food for thought, indeed!


DeCasien, A. R., Williams, S. A., & Higham, J. P. (2017) Primate brain size is predicted by diet but not sociality. Nature: Ecology & Evolution, 1, 0112.

Dunbar, R. I. M. (2009). The social brain hypothesis and its implications for social evolution. Annals of Human Biology, 36, 562–572.

González-Forero, M., & Gardner, A. (2018). Inference of ecological and social drivers of human brain-size evolution. Nature, 557, 554–557.

Logan, C. J., Avin, S., Boogert, N., et al. (2018). Beyond brain size: Uncovering the neural correlates of behavioral and cognitive specialization. Comparative Cognition & Behavior Reviews, 13, 55–90.

Roberts, W. A. (2012). Evidence for future cognition in animals. Learning and Motivation, 43, 169–180.

Rosati, A. G. (2017). Foraging cognition: Reviving the ecological intelligence hypothesis. Trends in Cognitive Sciences, 21, 691–702.

Seligman, M. E. P., Railton, P., Baumeister, R. F., & Sripada, C. (2016). Homo prospectus. New York: Oxford.

More from Edward A. Wasserman Ph.D.
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