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.
Some pregnant women experience a metallic taste in their mouth during the early stages of pregnancy, because of the hormone changes. It's also fairly common to crave certain foods, or go off certain foods, and have a heightened sense of smell.
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.