The primary basis for the evolution of antibiotic resistance in bacteria is the process of natural selection. When exposed to antibiotics, susceptible bacteria are killed, while resistant strains survive and reproduce. This leads to an increase in the prevalence of resistance genes within bacterial populations over time. Factors such as overuse and misuse of antibiotics in medicine and agriculture exacerbate this issue, creating an urgent challenge in public health. Understanding the mechanisms of resistance and promoting prudent antibiotic use are critical for managing this ongoing threat.