Intelligence in animals is hard to establish, but the larger the brain is relative to the body, the more brain weight might be available for complex cognitive tasks. Rather than simply measuring raw brain weight, the EQ formula makes for a ranking of animals. The ranking coincides better with the observed complexity of behaviour. Mean EQ for mammals is around 1, with carnivorans, cetaceans and primates above 1, and insectivores and herbivores below. It also puts humans at the top of the list. The relationship between brain-to-body mass ratio and complexity of behaviour is not perfect, because other factors also influence intelligence. These factors include the evolution of the recent cerebral cortex and different degrees of brain folding. This increase the surface of the cortex, which is positively correlated to intelligence in humans.