The origin of endothermy map on the phylogeny is within Mammalia and within Aves. Phylogeny aims to determine the evolutionary relationships between phyla. Evolutionary relationships of a species or group of species can be used to build taxonomic groups; the evolutionary history of species is depicted by a phylogenetic trees. Avian and mammalian endothermy results from elevated rates of resting, or routine, metabolism and enables these animals to maintain high and stable body temperatures in the face of variable temperatures.