Staphylococcus aureus is a pathogenic bacterium that can infect a wide range of host species, including humans. S. aureus has a particular protein that binds with hemoglobin from the host organism. Hemoglobin is the iron-containing protein used to transport oxygen in the blood. Since iron is important for growth, S. aureus have evolved the ability to absorb the iron from the host's hemoglobin. Different S. aureus strains preferentially infect different hosts and have different amino acid sequences at their hemoglobin-binding domains (Table 1; letters indicate different amino acids). In an experiment, different S. aureus strains were mixed with hemoglobin from macaque monkeys and their binding ability was measured (Figure 1). The differences in amino acid sequences contributed to the differential binding abilities observed. Table 1. Selected amino acid sequences and preferred host for four strains of S. aureus S. aureus Strain Amino Acid Sequence Host Species 1 Q Q F Y H Y A R S Species A 2 R Q A Y H Y A R T Species B 3 Q Q A Y H Y A R T Macaque 4 R Q A A H Y Q L T Species C Figure 1. Macaque hemoglobin binding ability of different strains of S. aureus Which of the following processes is most consistent with the differences in the amino acid sequences listed in Table 1 ?