Brain size is one aspect of animal anatomy and evolution. Both overall brain size and the size of substructures have been analysed, and the question of links between size and functioning—particularly intelligence—has often proved controversial. Brain size is sometimes measured by weight and sometimes by volume (via MRI scans or by skull volume). Comparisons among animals The largest brains are those of sperm whales, weighing about . An elephant's brain weighs just over , a bottlenose dolphin's , whereas a human brain is around . Brain size tends to vary according to body size. The r...