ABSTRACT: We were all taught that asexual bacteria reproduced by dividing into two identical daughter cells. Recent studies have shown that the daughters are asymmetrical. One daughter receives more damaged proteins and grows less quickly. The asymmetry is advantageous because the resulting growth variance increases the fitness off the lineage. This fitness advantage is analogous to yields that result from models of portfolio diversification in economics. Population models and data show that bacterial lineages transition from immortality to mortality depending on the intensity of damage. The lineage of daughters receiving more damage experiences decreasing growth rates that serve as a model for biological aging.