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environment of any living species on Earth, and the increase in our population over the last few centuries has seriously and dramatically changed the face of the Earth. We’ll study further how humans have changed the Earth in Chapter 10; meanwhile, the following information explores how humans are impacted by our growing population and by our impact on the planet. This information is not explicitly tested but is useful for understanding the interplay between humans and the biosphere. Four of the most significant factors that have contributed to the increase in the world human population are improved nutrition, the availability of clean water, newly implemented systems for sanitary waste disposal, and better medical care. Another significant factor is the increase in food production. Almost half of the Earth’s land surface is currently devoted to various ways of producing food for humans; specifically, 12 percent of the Earth’s land is composed of farms, 11 percent is composed of forests planted by humans, and 26 percent is used for grazing livestock! As we mentioned earlier, this enormous amount of food production takes its toll on the land, and we now face excessive and harmful erosion, in addition to a variety of environmental problems that have resulted from the wide-scale use of irrigation. Finally, the widespread use of pesticides and fertilizers for increased crop yields leaves large amounts of harmful chemical residues in the soil and water. In response to these problems, the agricultural industry is continuing to invent and promote soil conservation techniques, organic farming, more efficient irrigation methods, and genetically modified crops. However, these new techniques will need to be implemented in all countries in order to be effective globally. In many cases, new techniques introduce new problems—for example, crop sizes may increase, but pesticides must then be used in order to protect the larger crops. The use of genetically modified organisms (GMOs) is also controversial. Inserting strands of DNA that code for resistance to pests or for larger crop size may lead to less genetic diversity. This in turn can lead to the likelihood of crops being susceptible to future pests and diseases. Also, there is no clear data regarding the effect these GMOs may have on human health in the future. What Happens When There Aren’t Enough Resources? Our bodies need certain nutrients to keep them healthy and to help resist disease. Some nutrients, or macronutrients, are needed in large amounts. These include proteins, carbohydrates, and fats. Other nutrients are needed in smaller amounts; these are called micronutrients. Micronutrients include vitamins, iron, and minerals such as calcium. When people are deprived of food, one result is the onset of hunger. Technically speaking, hunger occurs when insufficient calories are taken in to replace those being expended. Malnutrition is poor nutrition that results from an insufficient or poorly balanced diet; those whose diets lack essential vitamins and other components often suffer from it. A third term used to describe those who aren’t receiving sufficient resources is undernourished. Undernourished people have not been provided with sufficient quantity or quality of nourishment to sustain proper health and growth. According to the Food and Agriculture Organization, or FAO, 795 million people on Earth are undernourished. Some 780 million of these people are living in developing countries, but, perhaps surprisingly, the remaining 15 million are living in developed nations. On the other hand, 38 percent of adults in the United States are considered obese and, globally, 2.1 billion people are overweight. Why does this dichotomy exist? While the reasons for hunger are many and complex, the simplest explanation for the problem is poverty. Our planet produces sufficient food to feed today’s world population, but many people lack the money to buy food or the resources to produce it. All over the world, human communities are trapped in a cycle of poverty, resource degradation, and high fertility. For example, in the first third of the twentieth century, Asia, Africa, and Latin America produced enough grain that it was not necessary for them to import it from other countries. However, because of their constantly increasing populations, all of these countries are now importing grain; this is an ominous sign of impending problems with hunger in these countries. Encouragingly, China, Tha