from Biology as Ideology by R,C. Lewontin (1991)

Science serves two functions. First, it provides us with new ways of manipulating the material world by producing a set of techniques, practices, and inventions by which new things are produced and by which the quality of our lives is changed. The second function of science, which is sometimes independent and sometimes closely related to first, is the function of explanation. Even if scientist are not actually changing the material mode of our existence, they are constantly explaining why things are the way they are. It is often said that these theories about the world must be produced in order, ultimately, to change the world through practice.

Yet it is remarkable how much important practical science has been quite independent of theory. One of the most famous examples of scientific agricultural change is the introduction of hybrid corn all over the world. Hybrid corn is said to be one of the great triumphs of modern genetics in action, helping to feed people and increase their well-being. Yet the development of hybrid corn and, indeed, almost all plant and animal breeding as it is actually practiced has been carried out in a way that is completely independent of any scientific theory. Indeed, a great deal of plant and animal breeding has been done in a way indistinguishable from the methods of past centuries before anyone ever heard of genetics.