Decoding Earth's Extraordinary Animal Forms: 7 Essential Rules
Scientists have established seven rules that explain the extreme shapes and sizes of animals. Bergmann's rule states that animals evolve to be larger in colder climates, while Allen's rule states that animals in colder climates have smaller appendages. The square-cube law imposes a limit on how big animals can get. The island rule suggests that animals on islands tend to evolve into giant or dwarf versions of their mainland relatives. Island birds evolve toward flightlessness, and deep-sea gigantism occurs in invertebrate animals. Rensch's rule describes a trend in sexual dimorphism.