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.
Having such a taste in your mouth can also be caused by medication or by a physical condition which triggers an upset in your body chemistry. Bleeding gums is the most common cause of a metal taste. common cause is from bleeding, because the pigment in red blood cells contains iron. If you bite your tongue by accident, suffer trauma to the mouth, or have gum disease which can cause spontaneous bleeding from inflamed gums, then you will likely have a metal taste for a while, or notice it now and again.