In animals, it is thought that the larger the brain, the more brain weight will be available for more complex cognitive tasks. However, large animals need more neurons to represent their own bodies and control specific muscles; thus, relative rather than absolute brain size makes for a ranking of animals that better coincides with the observed complexity of animal behaviour. The relationship between brain-to-body mass ratio and complexity of behaviour is not perfect as other factors also influence intelligence, like the evolution of the recent cerebral cortex and different degrees of brain folding, which increase the surface of the cortex, which is positively correlated in humans to intelligence. The noted exception to this, of course, is swelling of the brain which, while resulting in greater surface area, does not alter the intelligence of those suffering from it.