Is starting a new business more difﬁcult in an emerging industry or in a mature industry? The density dependent model of organizational ecology maintains that the industry’s age is irrelevant; the number of ﬁrms currently occupying the market niche determines the industry’s competitive structure. Nevertheless, population-level learning predicts historical asymmetry in entry barriers. Over time, the average ﬁtness of the surviving population members increases, making market entry more difﬁcult. At the same time, surviving organizations become increasingly spread out across the resource space, providing niches that new ﬁrms can exploit. Thus, industry-level evolution systematically alters the environment that both existing organizations and new ﬁrms face. I offer a new speciﬁcation for the founding rate model that synthesizes ecological and evolutionary perspectives. Tests of this model in the American automobile industry support its merit.