"Biston betularia" caterpillars also occur in two forms, each adapted to a different situation. They develop body colours which match the brown or green twigs of their host plant. This is done by a mechanism called polyphenism. Polyphenism is a kind of polymorphism where different forms of an animal are caused by the same genome. The animal inherits the capability, but the environment determines which form develops. This contrasts with genetic polymorphism of the adults, where each morph (form) inherits a slightly different genome.