The size of the human brain is substantially larger proportionally to the human body when you compare this to other animals. At 1350 centimetre cubed for an average man who weighs 58 kilograms, this is over twice as large as the homo habilis; an ancestor to the homo sapien or modern man. As this evolution was taking place, the modern man underwent several changes. The brain enlarged, but along with it, the human body got larger. The nutritional requirements of the human evolved to meet the new energy needs.
I don’t blame you for not having noticed before, but your famous jaw line, that angular structure that you think augments your looks, underwent significant change. No, it did not have anything to do with making you look attractive, it was to enable you to meet your new dietary regime. The new eating plan comprised of higher nutritional quality food including meat and fat. The new diet plan was unlike your ancestors like the great apes whose food primarily consists of leaves and barks. Think of it as a modern man discovering the latest nutritionist on the block.
These changes in diet and physical characteristics were iterative as evolution continued to do its job. The fat from the meat helped brain development, and the higher density energy from the meat helped increase mobility and physical capacity. All of this, combined with several environmental factors, made the homo sapien increasingly turn to the diet that forms part of our daily lives. No, the invention of croissants was still some time away, sorry!
In an adult, the brain can consume as much as thirty percent of your resting energy. Think of it as one meal directly feeding your brain. In children, this can be as high as sixty percent, the reason they are born with a higher percentage of body fat. The next time you doubt your intelligence, you might want to feel better by looking at what is on your plate.