Genetic Diversity

During the process of natural selection genetic diversity is maintained, but contrastingly in selective breeding the opposite holds true; genetic diversity is reduced! Recent studies have revealed that genetic variation occurs frequently in normal populations of any species and that even those genes that are deleterious and defective are preserved in the gene pool as so-called recessive genes (recessive gene traits are not visibly apparent unlike dominant genes). It is now believed that such genetic variability confers adaptive properties to a population in the event of extreme environmental change.

Thus mutative genes that confer minimal benefit today could play a significant future role in the survival of the species in which it occurs. This could explain why defective or mutative genes are preserved as recessive genes in a population's gene pool. A good example illustrating the beneficial role recessive genes can confer to a population is the case of the English Peppered moth.

Like a large number of insects the Peppered moth relies on its color to camouflage it from predators. The dominantly prevalent grayish color of the Peppered moth allows it to blend in with its environment which so happen to be tree trunks and lichen of like color. Although lighter and darker shades of the moth exist, few of such individuals survive for the simple reason their camouflaging abilities are less effective.

However with the advent of the industrial revolution in the late 19th century the resultant pollution darkened the tree trunks such that the minority recessive trait which conferred a darker shade of gray to the moths became dominant because such moths were then better able to avoid predation. As pollution levels subsequently decreased the tree trunks gradually reverted to their normal color and so also did the color of the Peppered moth revert back to its pre-industrialization gray. Thus once again the recessive dark-gray color in the moth reverted to its usual minority role!