Standard models of galaxy formation make specific predictions for how galaxy properties depend on environment. These predictions follow from the assumption that galaxy properties are entirely determined by the formation histories of the halos which host them, and that the distribution of dark halo masses is skewed towards large masses in dense regions. We describe two tests of this assumption which can be made with currently available data.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html