All organisms depend on their environments for energy and the materials needed to sustain life: clean air, potable water, nutritious food, and safe places to live. For most of human history, increases in longevity were due to improved access to these necessities. Advances in agriculture, sanitation, water treatment, and hygiene have had a far greater impact on human health than medical technology.
Although the environment sustains human life, it can also cause disease. Lack of basic necessities is a significant cause of human mortality. In 2004, lack of access to safe drinking water was responsible for 1.8 million deaths (mostly small children) from diarrhea. That same year, lack of adequate sanitation caused 160 million people to become infected with schistosomiasis, which can cause malnutrition and organ damage. Approximately 1.1 billion people currently lack access to safe drinking water, and 2.6 billion do not have proper sanitation. Environmental hazards increase the risk of cancer, heart disease, asthma, and many other illnesses. These hazards can be physical, such as pollution and food contaminants, or they can be social, including dangerous work conditions and poverty.
By contrast, activities that promote health and extend human life can have adverse environmental effects. For example, food production causes environmental damage from pesticides and fertilizers, soil salinization, waste produced by livestock, carbon emissions from food manufacturing and transportation, and overfishing. Health care facilities also have adverse environmental impacts. Hospitals use large quantities of electricity and fossil fuels and produce medical wastes. To prevent some diseases, it may be necessary to damage the environment. For example, malaria was eradicated in the United States and other developed nations in the 1940s and 1950s as a result of draining wetlands and spraying DDT to kill mosquitoes. A reduction in mortality from starvation or disease can lead to overpopulation, which stresses the environment in many different ways—increasing use of fossil fuels, clearing land, generating pollution and waste, and so on.
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