Evolution is not always a movement from simple to complex. In this section, we will analyze the mechanisms that allow species to thrive or, conversely, lead them to extinction. The basis of the topic is the classical macroevolutionary directions formulated by A. N. Severtsov: aromorphosis, idioadaptation, and general degeneration.
You will learn why morphological simplification is also a step toward biological success, especially for parasites, which you will encounter in detail in the medical biology course. We will also analyze parallel evolution, in which related taxa independently acquire similar traits, and biological regression, a state where a species rapidly loses its range and population size.
At colloquia, students are most often asked to give specific examples of aromorphoses in vertebrates, distinguish parallelism from convergence, and explain why parasitism is not a sign of biological regression. Carefully review the examples for each direction—this is the key to successfully mastering the topic.