An "Evolutionary Line" refers to the sequence of changes and adaptations that a species undergoes over time. This concept is central to the study of evolution, illustrating how organisms evolve from common ancestors through processes like natural selection and genetic drift. Each branch in the evolutionary line represents a divergence where species adapt to different environments or niches. In the context of phylogenetics, an evolutionary line can be depicted as a tree, showing relationships between various species. This tree helps scientists understand how traits and characteristics have developed and how closely related different organisms are, providing insights into the history of life on Earth.