I awoke this morning enveloped by a cotton t-shirt, cotton shorts, and cotton sheets. Now cotton socks, cotton jeans, a cotton shirt, and cotton underclothes clad me. You might spend much of your life swaddled in cotton, too. As we saw, we owe this comfortable fiber to the domestication of cotton some five thousand years ago. But that was not the end of the process. We also owe our comfort to breeders, who more recently modified the plant on purpose. So in living with cotton, we are surrounding ourselves with a product of intentional evolution.

The thesis of this chapter is that people have used a variety of techniques to modify the traits of populations intentionally, and they continue to invent new ones. The term intentional evolution does not imply that people thought, “I intend to affect the evolution of a species.” Few would have done so. Most have thought of themselves as doing something else such as breeding plants or animals. We will organize those actions by the evolutionary processes they affect. We will start with a pair of selective techniques: culling and methodical selection (breeding). Then we will turn to efforts designed to increase or decrease variation. These include hybridizing, transporting, acclimatizing, promoting mutations, genetic engineering, inbreeding, and cloning. We will examine methods that affect inheritance. In addition to three ways of influencing variation (cloning, genetic engineering, and promoting mutations), we will look at sterilizing. We will conclude by looking at a cousin of trait modification: extinction.