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.
A metallic taste in your mouth is a type of taste disorder known medically as parageusia. This unpleasant taste can develop suddenly or over longer periods of time. To understand what causes a metallic taste you must first understand how taste works. Your sense of taste is controlled by your taste buds and your olfactory sensory neurons.