What Mammals Have the Biggest Brains?

The largest mammalian brain belongs to the sperm whale, one of the biggest cetaceans in the sea. The sperm whale's head comprises 25 to 35 percent of its entire body length. The mature adult sperm whale's brain weighs an average of 18 pounds, and can grow to be nearly 500 cubic inches in size. For comparison, the human brain is only about 80 cubic inches. Compared to the exceptional size of the sperm whale, however, the brain itself is not that large: the brain mass is only .02 percent of the total body mass.

The brain of the elephant is the largest contained by any living land-dwelling mammal. The adult male elephant's brain can grow to be a whopping 12 pounds. As with the sperm whale, the brain accounts for relatively little of the elephant's total body mass. The elephant's brain accounts for roughly .1 percent of its mass, and is uniquely located at the back of its head, not at the front.

Dolphins, known as highly intelligent creatures, have a brain size and brain-mass-to-body-mass ratio much like that of humans. While the dolphin's brain weight is just above that of the human brain at 3.5 pounds, the brain makes up about 1.19 percent of the total body mass, slightly less than that of a human. A dolphin, like a human, has a large neocortex in comparison to other animals. The neocortex is the portion of the brain responsible for thinking and superior cognitive functions.

Humans make the list of largest brains by possessing a brain that can weigh up to 3.1 pounds, and that accounts for around 2.1 percent of the body. The human brain has three main parts: the cerebrum (forebrain), cerebellum (midbrain) and brain stem (hindbrain). The cerebrum contains the neocortex, and is the largest and most recognizable section of the brain. The human brain is divided into two hemispheres, and each controls the opposite side of the body: the left hemisphere controls the right side of the body, and the right hemisphere controls the left.