Relative brain size in monkeys and prosimians.

Prosimians have smaller brains relative to their body sizes than do monkeys. Brain and body weights, however, are associated not only on the basis of the brain integrating sensorimotor functions, but also on the basis of the body's requirement to support the energetic needs of the brain. Prosimians differ from monkeys in that they have lower rates of oxygen turnover. When body size is adjusted for its rate of oxygen turnover, monkeys and prosimians have equivalent relative brain sizes. A consideration of the brain's energy requirements helps to clarify brain-body relationships.