Memory T cells can be divided into central memory T cell (T_CM cell) and effector memory T cell (T_EM cell) subsets based on homing characteristics and effector functions. Whether T_EM and T_CM cells represent interconnected or distinct lineages is unclear, although the present paradigm suggests that T_EM and T_CM cells follow a linear differentiation pathway from naive T cells to effector T cells to T_EM cells to T_CM cells. We show here that naive T cell precursor frequency profoundly influenced the pathway along which CD8⁺ memory T cells developed. At low precursor frequency, those T_EM cells generated represented a stable cell lineage that failed to further differentiate into T_CM cells. These findings do not adhere to the present dogma regarding memory T cell generation and provide a means for identifying factors controlling memory T cell lineage commitment.