Diet and the Evolution of the Human Brain

human brain evolution

The evolution of the human brain has always been shrouded in mystery. This is because the organ tripled in size over the course of nearly seven million years, a pace of evolution that is unheard of in the natural world. Most of this growth occurred in the past two million years, during which time the brain doubled in size; although there was another major increase in volume, too, which took place between 500,000 and 100,000 years ago. The modern human brain is three times larger than the brains of our closest living relatives, chimpanzees and bonobos.

Many explanations have been put forward to explain the phenomenon of our unusually large primate brain. Evolutionary theorists have postulated that we needed to develop big brains in order to meet the demands of forming large social groups, hunting, and the use of tools. The consumption of psychedelic mushrooms has even been presented as an explanation (this is known as the Stoned Ape Theory). While the notion of magic mushrooms increasing brain size may seem outlandish, the idea that the consumption of particular foods is responsible is not so far-fetched. Indeed, diet may hold great explanatory value when it comes to the rapid expansion of human brain size.

Was Diet Responsible for the Evolution of Large Brains in Humans?

A 2017 study published in the journal Nature Ecology & Evolution has found that foraging for fruit may be responsible for the evolution of big brains in primates. These findings challenge the long-held hypothesis – ‘the social brain hypothesis’ – which posits that primates and humans evolved large brains in order to deal with complex social interactions. A study published in 2012 claimed to demonstrate that larger brain sizes can be driven by cooperation and teamwork. Scientists came to this conclusion by using computer models of artificial organisms with artificial brains. These organisms competed in various games, and researchers showed that the transition to a cooperative society leads to the strongest selection for bigger brains. The authors stated:

Our model differs in that we exploit the use of theoretical experimental evolution combined with artificial neural networks to actually prove that yes, there is an actual cause-and-effect link between needing a large brain to compete against and cooperate with your social group mates.

However, while cooperation can lead to big brains, this doesn’t mean that this kind of social behaviour was in fact responsible. In this 2017 study, researchers highlight that primates that eat fruit have around 25% more brain tissue than leaf-eaters with the same body weight. Co-author Alex DeCasien says that, “[fruit] is higher quality, it is more nutrient dense, it requires less digesting time, than the leaves.” Fruit-eating can provide more energy than leaf-eating, aiding brain growth.

But it’s not just eating fruit that leads to big brains, but foraging for it as well. After all, it takes brainpower to find fruit, log its location, know how to get into the fruit, and know when it’s ripe and ready to eat. DeCasien points out that this is much more demanding than eating leaves, which are present everywhere in the primate’s environment. She adds that a bigger brain may then allow for more complex social interactions.

Even though the study only looked at non-human primates, the results could also tell us a great deal about why humans evolved to have such big brains. Chris Venditti, an evolutionary biologist at the University of Reading, underscores that we are the only primate that can get a significant amount of calories from meat (because we cook it and so make it easily digestible). This extra energy in our evolutionary past could have given us more opportunities to grow larger brains. Previous research has suggested that eating meat and cooking food fuelled human brain evolution.

However, there are some issues with this new study. For example, researchers only looked at the relative brain size of different species. They didn’t analyse the size of the neocortex, which is involved in complex cognitive processes, such as perception, reasoning, and thought. So it could be that the size of the neocortex is related to group size and social interaction. Robin Dunbar, who is a proponent of the theory that social interaction drives brain evolution, reminds us of previous studies linking the size of the neocortex and group size in humans and monkeys.

Other Hypotheses About Diet and Human Brain Evolution

There are other hypotheses about how diet influenced the rapid evolution of the human brain. It has been proposed that access to DHA (an omega-3 fatty acid) during human evolution played a key role in increasing the brain/body-mass ratio. DHA is an important brain constituent – we need it for proper brain function and health – and this may support the idea that consuming fish (so a diet high in DHA) was necessary for the doubling of our brain size. Indeed, a range of evidence indicates that early hominids adapted to consuming fish and thus gained access to DHA before this explosion in brain size.

Dr Michael Crawford, the director of the Institute of Brain Chemistry and Human Nutrition at London Metropolitan University, believes that the brain dramatically increased in size five to seven million years ago, not because apes came out of the trees to hunt on the savannah, but because they arrived at the coast and found supplies of fish. However, there are some issues with this interpretation of human evolution. Firstly, five to seven million years ago brain size increased only slightly. The real jump was two million years ago to the present day – the doubling of brain size. Also, our hominid ancestors did not seem to be exclusively coastal. Other scientists have critiqued Crawford’s hypothesis based on the existing literature.

Future Brain Evolution

We are, of course, still evolving. Although, it is not clear how our brains will evolve. It looks like our brains are shrinking rather than getting bigger. So increases in intelligence will most likely come from utilising the biological hardware that we have in the most effective way possible. This could involve designing and using better smart drugs and supplementing our minds with a computer interface. Soon it might not be natural factors like diet or complex social interaction that determine huge increases in intelligence, but the merging of the human mind with artificial intelligence (although this may result in the loss of our personal identity).

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