It is a puzzle why the significance of Mendel’s paper Versuche über Pflanzen-Hybriden for the study of heredity was not well appreciated until the 1900s. This chapter revisits the problem of the long neglect and provides a new philosophical explanation. I begin with a distinction between two versions of the problem. I critically examine the traditional diagnoses of the problem. Then I defend the exemplar-based account of Mendel’s contribution. Finally, I further develop an exemplar-based explanation of problem of the long neglect.