<P> Brain size usually increases with body size in animals (i.e. large animals usually have larger brains than smaller animals); the relationship is not, however, linear . Small mammals such as mice may have a brain / body ratio similar to humans, while elephants have a comparatively lower brain / body ratio . </P> <P> 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, are those suffering from swelling of the brain which, while resulting in greater surface area, does not alter intelligence . </P> <Table> <Tr> <Th> Species </Th> <Th> Brain: body mass ratio (E: S) </Th> </Tr> <Tr> <Td> small ants </Td> <Td> 1: 7 </Td> </Tr> <Tr> <Td> tree shrew </Td> <Td> 1: 10 </Td> </Tr> <Tr> <Td> small birds </Td> <Td> 1: 14 </Td> </Tr> <Tr> <Td> mouse </Td> <Td> 1: 40 </Td> </Tr> <Tr> <Td> human </Td> <Td> 1: 50 </Td> </Tr> <Tr> <Td> cat </Td> <Td> 1: 110 </Td> </Tr> <Tr> <Td> dog </Td> <Td> 1: 125 </Td> </Tr> <Tr> <Td> squirrel </Td> <Td> 1: 150 </Td> </Tr> <Tr> <Td> frog </Td> <Td> 1: 172 </Td> </Tr> <Tr> <Td> lion </Td> <Td> 1: 550 </Td> </Tr> <Tr> <Td> elephant </Td> <Td> 1: 560 </Td> </Tr> <Tr> <Td> horse </Td> <Td> 1: 600 </Td> </Tr> <Tr> <Td> shark </Td> <Td> 1: 2496 </Td> </Tr> <Tr> <Td> hippopotamus </Td> <Td> 1: 2789 </Td> </Tr> </Table> <Tr> <Th> Species </Th> <Th> Brain: body mass ratio (E: S) </Th> </Tr>

List of animals by brain to body ratio
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