Evolutionary pressure or selection pressure can be formalized as an external pressure applied to a process, thereby pushing that process in a distinct direction.

A process driven by evolutionary pressure is, for example, the natural selection for erythrocytes carrying the sickle cell hemoglobin gene mutation (Hb S)—causing sickle cell anaemia—in areas where malaria is a major health concern, which grants some resistance to this infectious disease. Therefore, the concept can be described as the application of Charles Darwin‘s principle of “survival of the fittest” (which actually should be understood as “extinction of the un-fittest”) via some selection mechanism.

It is a quantitative description of the amount of change occurring in processes investigated by evolutionary biology, but the formal concept is often extended to other areas of research.

In population genetics, selection pressure is usually expressed as a selection coefficient. nl:Selectiedruk uk:Еволюційний тиск