By focusing on the crucial role of environment in the process of adaptation, Robert Brandon clarifies definitions and principles so as to help make the argument of evolution by natural selection empirically testable. He proposes that natural selection is the process of differential reproduction resulting from differential adaptedness to a common selective environment. Originally published in 1990. The Princeton Legacy Library uses the latest print-on-demand technology to again make available previously out-of-print books from the distinguished backlist of Princeton University Press. These editions preserve the original texts of these important books while presenting them in durable paperback and hardcover editions. The goal of the Princeton Legacy Library is to vastly increase access to the rich scholarly heritage found in the thousands of books published by Princeton University Press since its founding in 1905.