<P> Unlike the graph shown above which includes only mammals which are warm - blooded vertebrates, a graph of the relation between brain weight and body weight of living vertebrates including those that are cold - blooded (fish, amphibia, reptiles) shows that they have two completely separate linear functions . Cold - blooded vertebrates have much smaller brains than warm - blooded vertebrates of the same size . </P> <P> However, if physiology / metabolism is taken into account, the brain - to - body relationship of both warm and cold - blooded vertebrates fall on the same line with most of them using between 2 and 8 percent of their basal metabolism for the brain and spinal cord . </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>

Who has the largest brain in comparison to its size