Ehrlich's original idea of the selective theory for lymphocyte specificity postulated that a lymphocyte expresses many different antigen-specific receptors, with a foreign antigen or pathogen "selecting" one specific receptor. We now know that the outcome of clonal selection for B cells is the secretion of many copies of the same B-cell receptor in the form of a soluble antibody (humoral immunity). In what specific way was Ehrlich's original theory later refined? What are the challenges to aligning Ehrlich's original model with the above observation of humoral immunity? Does our current model of clonal selection fit this observation any better?