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.
Problem with the airways. A cold, sinus infection, runny nose from allergies (allergic rhinitis) or nasal polyps can all cause a metallic taste in the mouth. The links will take you to more information on these conditions. A wide range of medication can cause a metallic taste in the mouth as a side effect.