Abstract
This collection of essays by Robert Brandon spans two decades and most of the important problems in the philosophy of biology. Four of his five most important contributions to the philosophy of biology can be found here: the concept of relative adaptedness and its role in the propensity interpretation of fitness; the principle of natural selection; the use of the screening-off relation in defense of organismic selection; and the distinction between units of selection and levels of selection. The fifth major contribution, an analysis of the concept of "environment," mentioned briefly in an essay on the co-evolution of organisms and environment, is given an extended treatment in his 1990 book, Adaptation and Environment.