gradualism

noun

1. (countable, uncountable)The belief that evolution proceeds at a steady pace, without the sudden development of new species or biological features from one generation to the next.
2. (countable, uncountable)The belief that some phenomenon occurs gradually over a long period of time.

   “Given enough time, the logic goes, water can cleave solid rock and mountains can be reduced to plains. This "gradualism" now underpins modern geologic thought. ... Maybe we'll find evidence that the rock layers are exposed on the flanks of Mount Sharp [on Mars] not because a river carved through them over millions of years, but because the wind blew against them for billions of years – the ultimate in gradualism.”

3. (countable, uncountable)The belief that change ought to be brought about in small, discrete increments rather than in abrupt strokes such as revolutions or uprisings.