B-cells undergo somatic hypermutation and clonal selection in germinal centers — affinity to antigen improves over successive rounds.
Clonal selection (Burnet 1957): only B-cells that bind antigen are selected for proliferation. Affinity maturation occurs in germinal centers where somatic hypermutation + selection drives antibodies to picomolar affinity over ~2 weeks. Each "generation" here represents one germinal center cycle (~12h).