Pathogen evolution refers to the process by which harmful microorganisms, such as bacteria and viruses, change over time. These changes can occur through mutations in their genetic material, allowing them to adapt to new environments, evade the immune system, or develop resistance to treatments. This evolution can lead to the emergence of new strains that may be more virulent or transmissible. Factors influencing pathogen evolution include natural selection, genetic drift, and horizontal gene transfer. Environmental pressures, such as the use of antibiotics or vaccines, can accelerate these changes. Understanding pathogen evolution is crucial for developing effective public health strategies and treatments.