Biology textbooks say that animals of the same temperature in cold regions of the world are larger than those at the equator. A current study now provides evidence that this is not true. Is “Bergmann’s rule” wrong?
Bergmann’s rule is one of the principles of biology that should not be missing from any standard textbook. It states that equally warm animals that live in cold regions of the earth are larger than related species in warmer areas. For example, polar bears at the North Pole are larger than grizzly bears in Canada. The collared bear, which lives in Asia near the equator, is even smaller. This is due to the fact that as an animal grows larger, its skin surface area becomes smaller in relation to its body volume. Since body heat is lost across the surface, the relative heat loss decreases.