Biologists Richard Dawkins and Stephen Jay Gould have recently extended their decades-old disagreements about evolution to the issue of the nature and reality of evolutionary progress. According to Gould, 'progress' is a noxious notion that deserves to be expunged from evolutionary biology. In Dawkins' view, on the other hand, progress is one of the most important, pervasive and inevitable aspects of evolution. Simple appeals to 'the evidence' are clearly insufficient to resolve this disagreement, since it is precisely the interpretation of (...) the evidence that is in dispute. Scientific controversies in general, and the Dawkins/Gould dispute over evolutionary progress in particular, are worth examining in some detail because doing so sheds light on the interconnected roles of methodological and contextual factors in the formation, articulation and defense of scientific claims. My aim in this paper is to clarify the structure of the Dawkins/Gould dispute by analyzing it in terms of a tri-level model of scientific controversies, involving 'top-level' substantive disagreements, 'middle-level' methodological differences, and 'bottom-level' differences in historical and social factors. This simple three-tiered model is sufficiently abstract to have more general applicability to other scientific controversies. (shrink)