For centuries humans have used artificial selection on the phenotypes of domestic species. Current developments in molecular genetic engineering have the potential to completely alter agricultural methods. Nonetheless, there are a number of reasons why traditional agricultural improvement techniques must always be used with molecular genetics if one is to maximize the increase in the economic value of domesticated populations. Throughout the previous several decades, the rate of improvement of economically significant features, such as grain production in corn and wheat and milk yield in dairy cattle, has been between a few and several percent of the mean annually (Smith, 1988). It has been determined that for a variety of crop plants, environmental factors—i.e., environmental effects—rather than genetic changes—are responsible for around half of this improvement.