What theory proposes evolution occurs in tiny stages over long periods of time?

Hint: Evolution is a natural process that involves modifications in phenotype of a species depending upon the demands of nature. Such a change is generally beneficial for the entire species as it increases their chances of survival.

Complete answer:
The term evolution was coined by Jean-Baptiste Lamarck who proposed the theory of Transmutation of species. The theory that proposes the fact that evolution occurs in tiny stages over long periods of time was given by Charles Darwin. He gave the famous theory of evolution that helped in studying the origin of humans. He discussed this theory of evolution, in his book On the Origin of species. The book described evolution as a slow and steady process that is capable of modifying the individual in terms of its physical structure and their functions.

Charles Darwin was basically a naturalist who made a successful attempt to explain the concept of evolution. In his theory he considered that evolution helps the individuals of species to meet, fight and survive the natural hurdles. Nature keeps imposing certain challenges in front of every species at a regular interval of time. Those species who evolve as per the environmental demands are able to fight and survive against these hurdles while others become extinct. Darwin explained that evolution is a time consuming process as it takes ages to modify even minor physical structure.

Note:
Example of evolution in humans - Absence of wisdom teeth in upcoming generations. It is believed that wisdom tooth was a requirement for African ancestors who consumed hard food that was soon replaced with industrialisation as humans started consuming soft food which is thus, eventually leading to disappearance of the wisdom tooth.