When humans initially started farming, they used selective breeding to pass on desirable traits of the crops while omitting the undesirable ones. Selective breeding leads to monocultures: entire farms of nearly genetically identical plants. Little to no [Genetic diversity]Create? makes crops extremely susceptible to widespread disease. [bacteria]Create? morph and change constantly. When a disease causing [bacteria]Create? changes to attack a specific genetic variation, it can easily wipe out vast quantities of the species. If the genetic variation that the bacterium is best at attacking happens to be that which humans have selectively bred to use for harvest, the entire crop will be wiped out. ("Introduction to Genetic Diversity." Cheetah Conservation Fund. 2002. 19 Mar. 2008 www.cheetah.org)
A very similar occurrence is the cause of the infamous Potato Famine in Ireland. Since new potato plants do not come as a result of reproduction but rather from pieces of the parent plant, no [Genetic diversity]Create? is developed, and the entire crop is essentially a clone of one potato, it is especially susceptible to an epidemic. In the 1840s, much of Ireland’s population depended on potatoes for food. They planted namely the “lumper” variety of potato, which was susceptible to a rot-causing mold called Phytophthora infestans. ("Monoculture and the Irish Potato Famine." Understanding Evolution. Berkley University. 19 Mar. 2008 ) This mold destroyed the vast majority of the potato crop, and left thousands of people to starve to death.
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