The following question refers to the figure.
In an eight-year experiment, a population of E. coli, begun from a single cell, was grown in low-glucose conditions. The culture was transferred to fresh growth medium every 24 hours. Periodically, samples were removed from each population and the ability to survive in low-glucose conditions was compared with the original (ancestral) E. coli population.
The cells in the cell line grown in low-glucose conditions showed the effects of which of the following processes?