The Hardy-Weinberg principle is not generally found in nature because it requires certain conditions in an environment. These conditions are the absence of the things that can cause evolution. In other words, if no mechanisms of evolution are acting on a population, evolution will not occur--the gene pool frequencies will remain unchanged.
Gum disease is a very common condition where the gums become swollen, sore or infected. The gums tend to bleed after you brush or floss your teeth, and the blood in your mouth causes the metallic taste. If left untreated, the tissues and bone that support the teeth can also become affected (known as periodontitis).
Cancer chemotherapy medications may also produce a metallic taste in the mouth as a side effect. Metallic taste in the mouth can also arise due to a disorder of the nerves that control taste sensations. The condition of altered sense of taste is medically known as dysgeusia. Dysgeusia can cause a number of different alterations in taste, including a metallic taste. Some common medical conditions that can cause metallic taste in the mouth include ear or upper respiratory infections such as sinusitis, as well as head injury or conditions that damage the central nervous system (CNS). A history of radiation therapy to the head and neck can also cause a metallic taste in the mouth.