Phylogenetics
Phylogenetics is the study of the evolutionary relationships between biological entities grouping species based on their genetic similarities. It assumes the existence of a common ancestor between two or more groups before its descendants drifted away from each other through evolutionary processes. When a population diverges from their ancestors and their genome is different enough, a new species arises. This complex concept driven by multiple factors is called speciation.
Phylogenetic analysis is based on the comparison of conserved hereditary sequences. The outcome of this is often shown as "phylogenetic trees", with branches representing each species and nodes representing their common ancestors. These studies can be used to determine the evolutionary distance of DNA sequences or even entire organisms.