> Still, the brain grew to maybe 2-4 times the size over this period. I read somewhere that the human brain makes up only about 2% of body weight but uses 20%

> Still, the brain grew to maybe 2-4 times the size over this period. I read somewhere that the human brain makes up only about 2% of body weight but uses 20% of the body’s energy. While brain size has increased over time, brain size does not determine intelligence. The brain’s high energy use, constant activity, and complex processes are more important. Its metabolic activity, continuous glucose and oxygen consumption, neurotransmitter dynamics, and synaptic plasticity all play major roles in cognitive function. Intelligence is shaped by the brain’s efficiency, how well it forms and adjusts neural connections, and the energy it invests in processing information. Intelligence depends far more on how the brain works than on its size.