Kuhn made two attempts at providing an evolutionary analogy for scientific change. The first attempt, in The Structure of Scientific Revolutions, is very brief and unstructured; in this article I discuss some of its weaknesses. Alexander Bird takes this attempt more seriously and provides a criticism based on oversimplified evolutionary assumptions. These assumptions prove to be inadequate for the second, more articulate, evolutionary analogy suggested by Kuhn in “The Road since Structure.” I argue, however, that this second Kuhnian attempt is undermined by his inadequate view of biological progress and by his misunderstanding of the concept of ecological niche.