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	Reciprocity Scientists sometimes speak of a "web of life" or a "food web". This is misleading in at least two ways. A web consists of static connections between components, whereas the relationships we observe and participate in consist of a continual dynamic flow of goods and services exchanged between players. And the players include the sun, the clouds, rivers, oceans, and rocks as well as what we normally consider living things. Here the components of earth and sky are grouped in the center, surrounded by the digesters, the plants, and the animals. Goods and services flow sunwise between groups, a giving path and a receiving path. This is sometimes called reciprocity: to get value you must give value. When you expand a group, you can examine the internal reciprocity among the players inside (for example, carnivores eat herbivores), as well as the ways in which each player processes the goods it receives. Plants and animals produce "waste", which is food for the digesters; the digesters are the only group which actually gets food from rocks (and soil minerals), and they produce food for everyone else. This picture is very abstract; it is important to remember that reciprocity occurs between real individuals in a real place.