By Sirena Khanna
Food is often on our minds. We are the only species that watches competitive baking, eats tropical fruit in freezing climates, and adorns our food with gold. The mass production, transport, and consumption of foods from all over the world are feats that can only be derived by the human brain, and as it turns out, food is what helped shape our brains in the first place.
The story starts 1.9 million years ago when our ancestors, Homo erectus, first appeared in Eurasia (as the most recent fossil evidence suggests). Raw meat, as well as vegetables and fruit, were staples of the hominid diet. One day, our ancestors made a great culinary advancement and cooked meat entered the scene. By chance or tasteful insight, H. erectus combined meat and fire, and in the process created the world’s first barbeque.
Prehistoric cookouts were a success. H. erectus developed brains twice the size of their predecessors, H. habilis, and their teeth and body size decreased to about the size of a modern human’s. This is the basis for Richard Wrangham’s “cooking hypothesis,” which attributes the dramatic increase in H. erectus brain size that occurred 500,000 years ago to the advent of cooking. This newfound ability may have prevailed, he posits, because it allowed H. erectus to save a significant amount of time and energy that would otherwise have been spent on chewing raw meat.
Wrangham collected data on chimpanzees and found that they can spend up to 5 hours a day gnawing on fruit. At the chimpanzee’s chewing rate, H. erectus would have had to spend a quarter of their lives chewing and another quarter gathering food to sustain their energy needs if they did not cook their meat. Lucky for modern humans, H. erectus were the master chefs of hunter-gatherer society; cooking meat altered the chemical structure of proteins and starches such that it was easier to break down. Wrangham postulates that cooked meat expedited digestion, as evidenced by a decrease in gut size. The energy saved from digestion went into spurring the encephalization of H. erectus.
Wrangham’s hypothesis is a good start to explaining the sudden change in hominid brain size. There is, however, one complication: the discovery and use of fire. Some skeptics maintain that H. erectus did not control fire until 200,000 years ago, which doesn’t coincide with the “cooking hypothesis” timeline. Scientists are currently searching for evidence of man-made fires to investigate whether fire use did exist at the time of hominid brain expansion; however, fire use is difficult to pinpoint, as early hominids may have interacted with natural fires to cook before learning to control fire.
In the meantime, researchers Katherine Zink and Daniel Lieberman recently published a study that claims sliced meat might be responsible for the decrease in hominid teeth and jaw size. Similar to cooking, slicing meat makes meat easier to chew by breaking down the tissue and making the nutrients more accessible. Early hominids began to use stone tools at least 3 million years ago, so this timeline suggests that H. erectus used tools to slice their meat before they learned to cook it. The two proposals are not mutually exclusive, though: it is possible that slicing meat contributed to a decrease in tooth and jaw size, and later on cooked meat further propelled that shift.
The “expensive tissue hypothesis” also attempts to explain the physiological changes in H. erectus. It presents the paradox of having a metabolically expensive brain while maintaining energy-consuming organs. This hypothesis proposes that encephalization and reduction in gut size is only possible due to a diet of high-quality and easy to digest foods, such as various animal products like meat and bone marrow. Although the “expensive tissue hypothesis” does not focus on cooked or sliced meat, it does concur with the other postulates that animal product additions to the hominid diet were essential for the evolution of a larger human brain.
Whether sliced meat, cooked meat, or high-quality diets spurred larger brains is the primeval kitchen battle yet to be resolved. The growth could be due to a multitude of factors, so perhaps, on this cooking show, everyone wins. Over time, hominid teeth and gut size decreased while the brain steadily grew larger, especially the neocortex, a part of the brain’s center for higher cognitive functions. In terms of sheer size, the H. erectus ancestors, H. habilis, who lived 2 million years ago, had mature brain sizes of about 610 cubic centimeters; in comparison, the average adult human now has a brain size of 1,400 cubic centimeters.
Why does an increase in brain size matter? The general idea might be that bigger brains are better, but size is not everything. Neuroscientists Randy L. Buckner and Fenna M. Krienen propose that as hominid brains expanded, the tether-like network of neurons was ripped apart, allowing neurons to form new circuits. They call this the “tether hypothesis,” which elegantly explains why brain expansion matters for the evolution of brain function. Brain size alone, however, does not distinguish us from other species. Blackfish dolphins have twice as many neurons in the neocortex as humans, but their overall cognitive ability is not above a human’s.
Since there is no correlation between cognitive performance and the number of neocortical neurons, our superior cognitive abilities must be due to a combination of factors other than sheer brain size. There are many aspects of brain composition to consider, such as the sophistication of neural synapses and metabolism, the latter of which relates back to the three hypotheses about changes to the hominid diet. Changes to hominid diet, such as cooked or sliced meat, ultimately made energy consumption more efficient and fruitful for our ancestors. Greater energy-yielding diets led to gut, teeth, and jaw size reduction, while providing the energy for encephalization. As the only species that cooks, it is humbling to think that our relationship to food put us on a different cognitive trajectory than the rest of the animal kingdom.
Thanks to our ancestor’s penchant for firing up the grill, we can do things no other animal has come close to. But whereas meat-eating was an important factor in getting hominids to this point, the rampant consumption of meat is currently undoing humanity. Greenhouse gases produced by the processing and transportation of animal products threaten both humans and the environment, and antibiotics and hormones in meat give rise to health concerns like cardiovascular disease and undesirable genetic mutations. Nevertheless, meat consumption allowed our ancestors to develop larger brains that shaped who we are as humans today. As a tribute to our early cooks, we can imagine new ways to better our brains that do not rely on consuming meat at our current rate. If our ancestors could invent the barbecue with their small brains, then there is no doubt that bigger brains, with more tools, can achieve anything.