Habermas's theory of social evolution has been subjected to critique by environmentally motivated sociologists. They argue that his decision to recast social theory in terms of an extended, if selective analogy with biology leads him into a set of practical positions that are irreconcilable with Green politics and inconsistent with the goals of traditional critical theory. This article argues that these criticisms are based on an inaccurate assessment of the role of evolutionary concepts in Habermas's thought. By drawing out the similarities between Habermas and Kant on the question of the relationship between history and natural history, it is possible to see that Habermas's use of evolutionary metaphors plays a regulative rather than a constitutive role in his thinking on society. This strategy does not save Habermas's position, but shows instead that it may be vulnerable to an immanent critique that pulls out the real underlying antagonisms in his system. Copyright © 2003 SAGE Publications and Thesis Eleven Pty Ltd.