THE PROXIMATE ULTIMATE DISTINCTION IN THE MULTIPLE CAREERS OF MAYR,ERNST/

Ernst Mayr's distinction between ''ultimate'' and ''proximate'' causes is justly considered a major contribution to philosophy of biology. B ut how did Mayr come to this ''philosophical'' distinction, and what r ole did it play in his earlier ''scientific'' work? I address these is sues by dividing Mayr's work into three careers or phases: I);Mayr the naturalist/researcher, 2) Mayr the representative of and spokesman fo r evolutionary biology and systematics, and more recently 3) Mayr the historian and philosopher of biology. If we want to understand the rol e of the proximate/ultimate distinction in Mayr's more recent career a s a philosopher and historian, then it helps to consider his earlier, use of the distinction, in the course of his research, and in his prom otion of the professions of evolutionary biology and systematics. I be lieve that this approach would also shed light on some other important ''philosophical'' positions that Mayr has defended, including the dis tinction between ''essentialism: and ''population thinking.''