Another major impact of human activities is the acceleration of the evolutionary process for hundreds of bacteria and viruses. Many of these changes have occurred over a single human generation (that is, during the lifetime of many people living today), not the millions of years usually associated with evolution. As noted earlier, our use of antibiotics has dramatically altered the course of evolution of several bacterial diseases to the point where many bacteria have become resistant to antibiotics. Antibiotics have now become the most significant selective factors causing many bacteria to evolve into more virulent forms. It’s even likely that human technology and lifestyles are responsible for the deadly nature of some of the so-called new diseases that have arisen in recent decades, such as HIV/AIDS, dengue hemorrhagic fever, Legionnaires’ disease, Lyme disease, and resistant strains of Mycobacterium tuberculosis, Staphylococcus, and Escherichia coli. We could reach a point where we have no antibiotics capable of fighting dangerous bacteria that live and constantly mutate in our midst. For example, there are billions of beneficial bacteria in a person’s digestive tract. We couldn’t live without these bacteria, but some can and occasionally do mutate into varieties that cause serious illness and even death. Without antibiotics, these and many other bacteria in our environment would have the ability to drastically increase mortality due to infectious disease.
A similar phenomenon has occurred with the overuse and misuse of insecticides and pesticides on agricultural crops (Palumbi, 2001). As mentioned previously, DDT is perhaps the best-known insecticide to have altered the course of a species’ evolution. When this insecticide was first developed, it was hailed as the best way to reduce malaria by eliminating the mosquitoes that transmit the disease. DDT was highly effective when it was first applied to mosquito-ridden areas, but soon mosquitoes had evolved resistance to the powerful agent, rendering it almost useless in the fight against malaria. Moreover, the use of DDT proved disastrous to many bird species, including the bald eagle (Fig. 17-8). In the 1970s, its use was curtailed and even banned in some countries, but the failure of other efforts to treat malaria has led to a recent call to begin using DDT again.
From these examples, it’s clear that the human-caused accelerated process of microbial evolution is something that can lead to great harm to our species and the planet. Certainly none of the scientists developing anti biotics, insecticides, pesticides, and other biological tools intend to cause harm. But unless they understand the evolutionary process, they may not be able to foresee the long-term consequences of their work. As the great geneticist Theodosius Dobzhansky (1973) said, “Nothing in biology makes sense except in the light of evolution.” Indeed, we can’t afford to have even a single generation of scientists who are not fully informed about evolution. If human actions can cause an organism to evolve from a relatively benign state to a dangerously virulent one, there is no reason why we can’t turn that process around. In other words, it is theoretically possible to direct the course of evolution of a dangerous virus such as HIV to a more benign, less harmful state (Ewald, 1999).