Nucleic acid sequencing methods, which determine the order of nucleotides in DNA fragments, are rapidly progressing. These processes yield large quantities of sequence data—some of which is dynamic—that helps researchers understand how and why organisms function like they do. Sequencing also benefits epidemiological studies, such as the identification, diagnosis, and treatment of genetic and/or contagious diseases. Advanced sequencing technologies reveal valuable information about the time evolution of pathogen sequences. Because researchers can estimate how a mutation behaves under the pressure of natural selection, they are thus able to predict the impact of each mutation—in terms of survival and propagation—on the fitness of the pathogen in question. These predictions lend insight to infectious disease epistemology, pathogen evolution, and population dynamics.