Phyletic gradualism

Definition
noun
A theory stating that evolutionary change happens slowly, steadily and gradually in an attempt of the species to continue to adapt to new challenges over the course of their history until they became (gradually) new species different from their ancestors.
Supplement
Foraminiferans, a tiny species of marine animals living in Indian ocean, are said to demonstrate this process of evolution. The species remained relatively unchanged from about 10million to 6 million years ago then began a slow modification lasting about 600 000 years till they became an entirely new and different species from their ancestors.