The cellular progeny of a clonally selected lymphocyte must execute function. However, their function must often occur in more than one way, in more than one place and at more than one time. Experimental evidence supports the view that a single activated lymphocyte can produce a variety of cellular descendants. The mechanisms that are responsible for generating diversity among the progeny of a single lymphocyte remain a subject of lively controversy. Some groups have suggested stochastic mechanisms that are analogous to the diversification of the antigen receptor repertoire. We suggest that the complexity of lymphocyte fates in space and time can be derived from a single naive lymphocyte using the principles of cell diversification that are common in developmental and regenerative biology, including (but not limited to) asymmetric cell division.