Some, such as water and vegetables, are essential for human life. Others, such as iron and coal, are particularly useful to human beings. A few resources, including gold and uranium, are more valuable because they are scarce. Others, such as sand or air, are widely available and have a correspondingly low exchange value. The relative value of a commodity is dependent on two factors—how much of it there is and how much it is wanted. Economists call this the law of supply and demand. Commodities are often acquired where they are abundant and cheap and transported to regions where they are scarce and expensive, being exchanged there for valuable goods and services.

The human world today can be viewed as a vast network in which people produce, transport, exchange, and consume resources, commodities, and even ideas. While one region produces grain, another produces petroleum, and a third manufactures heavy machinery. Each depends on the products of the other two. Residents of each region seek to maximize the value of their own products and to obtain the products and resources they lack for the lowest possible price. Some regions are extremely active within this world system, maintaining vigorous trading relationships with every region willing to participate. Others are almost isolated from it, engaging in limited trade with only one or two neighbouring regions.

COMPLEXITY AND INTERDEPENDENCY
Since its creation, the world has developed into an increasingly complex system. All the world’s life forms are part of that system, consuming and producing resources in various ways. Humanity is also part of this system, and advancing technology has expanded the role of human activity in the world system. Unlike other inhabitants of the planet, however, humanity has become uniquely aware of its surroundings. As human understanding of the world expands, our ability to observe patterns and trends, and to predict future developments, is enhanced. This knowledge gives us the power to make decisions based not only on our immediate needs, but also on the probable future impact of our actions. In order to improve our ability to make good decisions, it is important for each of us to learn as much as we can about the world and the people with whom we share it.