There is simply no compelling reason we know of to explain why human brains got large,' says Tattersall. Huge brains are demanding organs: they make up only 2 per cent of the body's mass, but devour 20 per cent of its energy42. They are also comparatively picky in what they use as fuel. If you never ate another morsel of fat, your brain would not complain because it won't touch the stuff. It wants glucose instead, and lots of it, even if it means short-changing other organs.
Tattersall highlights a significant question regarding the evolution of the human brain's size, suggesting there is no strong explanation for why it became so large. Despite composing just a small part of total body weight, the brain requires a significant amount of energy to function, consuming around 20 percent of the body's energy resources. This raises intriguing concerns about the evolutionary advantages of such energy-intensive organ development.
Moreover, the brain's selective energy needs further complicate its evolutionary mystery. Unlike other organs, it primarily relies on glucose for fuel and does not utilize fats, prioritizing its energy demands even at the expense of other bodily functions. This unique dependency indicates a highly specialized evolutionary path, encouraging ongoing analysis of how such a demanding organ could have provided advantages that justified its development.
