A million or more years ago, in Africa, we started to become something very different from anything ever seen on the planet—and we did it by eating. We became creatures that had much bigger brains than any animal had ever needed. Also, our brains increased in size at a rate that far exceeded anything that evolution had been able to manage before.
How we accomplished this is the source of some argument. That's because there are (at least) three separate ways of looking at this process—and while they all arrive at the same destination, they take different routes. The hypothetical causes of our sudden brainy development distinguish each explanation from the others.
Let’s begin with the trendiest (at least among non-scientists) one. In recent years, after thinking about our condition and how we got here—“here” meaning overweight and unhealthy—many people have adopted the Paleo Diet. They place on our modern, starchy diet. They assume that, before the advent of cereal agriculture, our hunter-gather forebears had a diet that was high in meat protein (and, obviously, devoid of all sorts of chemicals found in food today). They reason that, if we could only go back to a so-called “caveman diet,” we could return to our former state of good health.
The Paleo argument goes something like this:
“Once our species got a taste for meat, it was provided with a dense, protein-rich source of energy. We no longer needed to invest internal resources on huge digestive tracts that were previously required to process vegetation and fruit, which are more difficult to digest. Freed from that task by meat, the new, energy-rich resources were then diverted inside our bodies and used to fuel our growing brains.
As a result, over the next two million years our crania grew, producing species of humans with increasingly large brains—until this carnivorous predilection produced Homo sapiens.” Source
If we choose to ignore the fact that we live a lot longer than our Stone-age ancestors (in itself, a fairly good argument against the Paleo Diet), one look at our teeth—and comparisons with the teeth of our ancient ancestral species—is enough to prove that we are meant to eat a varied diet, and reveals our evolution from ape-like vegetarians to all-consuming omnivores. Also, our smaller guts and bigger brains mark us as distinctly different from our hairier past.
It’s true that added high-protein flesh and calorie-rich fats could explain the sudden growth-spurt in our crania. However, the development of social systems that permitted cooperative hunting techniques might also have led to our increased intellectual development. It’s not always so easy, separating cause and effect.
But is a carnocentric diet the only possible explanation for the sudden development of big brains, and simultaneous diminution of teeth and digestive tracts? Some scientists question the premises of the Paleo dieticians:
“...archaeological, anthropological, genetic, physiological and anatomical data [indicate] carbohydrate consumption, particularly in the form of starch, was critical for the accelerated expansion of the human brain over the last million years…” Source
This idea is especially appealing (considering the much later effect that cereal agriculture had on the development of civilizations—a distinguishing feature of our species, even over other social species), but it runs into another problem. If plant-based foods, even those with lots of caloric starch, were the reason for our larger crania, how do we explain the changes to our teeth and abdomens? No herbivores have demonstrated such radical changes to their mental equipment. That’s because raw plant material must be consumed in large quantities, and requires large expenditures of digestive energy to extract their nutrients. Exclusively plant-eating creatures tend to have large teeth and bellies.
Which brings us to the third explanation:
“[Richard] Wrangham’s book Catching Fire: How Cooking Made Us Human … makes the case that the ability to harness fire and cook food allowed the brain to grow and the digestive tract to shrink, giving rise to our ancestor Homo erectus some 1.8 million years ago.” Source
Cooking made hard-to-digest foods—like starchy roots and grains—more easily assimilated. In effect, fire acted as an external digestive system, allowing us to get much more energy from our food without having to expend our own energy to do so. Recently, archaeologists have found evidence of ancient fires—pushing the time-frame for cooking into the 1-2 million year range of the other two explanations:
“…the remains of campfires from a million years ago—200,000 years older than any other firm evidence of human-controlled fire… fanned the flames of a decade-old debate over the influence of fire, particularly cooking, on the evolution of our species’s relatively capacious brains. “Source
Of course it also made that carefully-hunted meat taste even better.
Perhaps the conflicts between these approaches should be abandoned in favor of a shared explanation.
Perhaps our exponential growth of gray matter is a result of the confluence of multiple adaptations.
Perhaps we developed big brains by thinking about eating. Imagine a bunch of hominids, sitting around a campfire on the savannah, planning the next day’s hunt or foraging expedition, while sharing a roasted haunch of wildebeest, passing the boiled root-vegetables, and apishly grinning their satisfaction over a dessert of some ripe berries.
Eating, and planning our meals, together made us human.