The brains of humans are not the biggest compared to all other animals. The average human brain has a mass of about 1 kg. In contrast, the brain of a sperm whale has a mass of 8 kg and that of an elephant has a mass of 5 kg. You may be tempted to think that bigger brains means smarter and that because humans are the smartest animals, we must have the biggest brains. But biology does not work that way. When an animal has a larger overall size, all of its organs must be generally bigger just to keep it alive. A sperm whale weighs 35 to 45 metric tons and stretches about 15 meters long. With so much biological tissue to take care of, the sperm whale needs a giant heart to keep blood pumping to all this tissue, giant lungs to provide oxygen to all this tissue, and a giant brain to coordinate it all. The sperm whale needs a giant brain not because it is intelligent, but because it has so much low-level functions to carry out with such a huge body.