How does the dolphin brain compare to the human brain?
Whales and dolphins have quite large brains. Most authors agree that the size should be viewed in relation to the body size. In some comparisons, brain weight to body weight ratio is used, but it is now more common to use the so-called Encephalization Quotient (EQ), which is calculated as: EQ = brain weight / (0.12 * (body weight (2/3))) (brain weight, divided by 0.12 time the body weight to the power (2/3)). In this formula, brain and body weight should be expressed in grammes. In bottlenose dolphins, the EQ lies between 4 and 5, in the killer whale between 2.5 and 3, in humans in the 6.5-7.5 range. However, the structure of the dolphin brain is quite different from most land mammals and shows a lot of similarities with so-called archetypal mammals like hedgehogs and bats (mammals in which the brain structure has changed little since the middle of the Tertiary period). Dolphin and whale ancestors returned to the sea 50-70 million years ago. (Bats have presumably developed their aerial
