In this paper, I develop a naturalistic conception of evolutionary progress. I argue that the Waddingtonian notion of adaptability can be embedded meaningfully into a framework which views living things as nonequilibrium structures. This thermodynamic interpretation places great emphasis on the dynamics of environmental change, whereas the classical conceptions are based on equilibrium conceptions of the evolutionary process. What improves in evolution is the ability of living things to stay alive in increasingly heterogeneous environments.