In 1847, the German biologist Christian Bergmann noted that mammals and birds living at higher latitudes (farther from the equator) are on average larger and bulkier than related species found at lower latitudes. Suggest an evolutionary hypothesis to explain this observation.
not quite sure how to do the hypothesis but its likely to be something to do with the fact that they need more fat and muscle due to the thinner atmosphere as respiration is harder to occur.
