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).
Plaque buildup, gingivitis, periodontitis, tooth decay and abscesses can produce a bad taste in your mouth, which may be experienced as a metallic taste. Sinus infections and medicines or illnesses that cause dryness of the mouth, such as lichen planus and sicca syndrome, can also sometimes lead to a metallic taste.