The genesis of racial predisposition to disease is a subject infrequently discussed or all too often dismissed with the statement, in most cases quite obvious, that the tendency is hereditary. In great part, this is probably due to the impossibility, at present, of putting hypotheses on this subject to experimental or statistical proof and to the reluctance on the part of modern scientific workers to recognize the importance of such tentative opinions. But, since in reality hypotheses play so important a rôle in scientific medicine,1it is without apology to experimental science that I offer this possible explanation for the marked predisposition of the Negro to keloid formation. In this hypothesis the principle of sexual selection makes, so far as I know, its first appearance in pathology. Keloid occurs as an uncommon sequela to injury to the skin. Whether the division into "true" and "false," or traumatic and nontraumatic,