The brain volume largely correlates to body size [0] in mammals. More muscle cells require more nerves to control them which requires more coordination and henc

The brain volume largely correlates to body size [0] in mammals. More muscle cells require more nerves to control them which requires more coordination and hence a larger brain. How the mammalian brain divies up this process depends on enviromental factors and the body plan. Dolphins and whales have specific parts of the brain used for ecolocation and the water pressure affects the volume of the brain. Elephants have larger areas devoted to using their trunk. Aye-Ayes have large visual cortices as they hunt inscets in the dark for food. [0] https://en.wikipedia.org/wiki/Brain_size https://en.wikipedia.org/wiki/Brain_size