Adaptations enable living organisms to cope with environmental stresses and pressures. Adaptation can be structural or behavioral. Structural adaptations are special body parts of an organism that help it to survive in its natural habitat (e.g., skin color, shape, body covering). Behavioral adaptations are the ways a particular organism behaves to survive in its natural habitat. Physiological adaptations are systems present in an organism that allow it to perform certain biochemical reactions (e.g. making venom, secreting slime, being able to keep a constant body temperature). Adaptations are traits that have been selected for by natural selection. The underlying genetic basis for the adaptive trait did not arise as a consequence of the environment; the genetic variant pre-existed and was subsequently selected because it provided the bearer of that variant some advantage.