 Other ecogeographical rules include Bergmann's Rule, coined by Carl Bergmann in 1857, which states that homeotherms closer to the Equator tend to be smaller than their more northerly or southerly conspecifics.One of the proposed reasons for this cline is that larger animals have a relatively smaller surface area to volume ratio and therefore improved heat conservancy – an important advantage in cold climates.The role of the environment in imposing a selective pressure and producing this cline has been heavily implicated due to the fact that Bergmann’s Rule has been observed across many independent lineages of species and continents.