Evolution is unpredictable and irreversible, biologists show

A study by biologists now provides evidence that, at the molecular level, evolution is both unpredictable and irreversible. The study focuses exclusively on the type of evolution known as purifying selection, which favors mutations that have no or only a small effect in a fixed environment. This is in contrast to adaptation, in which mutations are selected if they increase an organism’s fitness in a new environment. Purifying selection is by far the more common type of selection. —> Read More